I have not seen or heard either a 1500 or a 2500, but I have looked at the manuals and the extended code sets on the Yamaha website. From that, I have drawn some conclusions, which may or may not be right. This list is not meant to be exhaustive, but rather some intersting things I noticed.
The 1500 looks like a combination of the old 1400 and 2400 with some minor improvements. Compared to the 1400, it has more power (like the 2400), an RS-232 interface (like the 2400), a new front panel display (volume in dB rather than a bar graph, PLIIx light added and some minor re-arranging), the RS-232 portfrom the 2400 has been added to the rear panel (which otherwise looks like a 1400), and it has a new remote. The remote includes macro capabilities as well as the ability to access "optional" discrete functions like the 2400 remote could, but which was not available on the 1400 remote. Audio delay/lip sync is still not on the remote. If you look at the new RS-232 control codes, they even reference the 2400 in one place, making it pretty clear that the 1500 is mostly a mix of the 1400 and 2400. Additionally, the lack of the new PLIIx discrete extended IR codes (available on both the 750 and the 2500) and input trim - see below - supports that conclusion. The 1500 does have new 19kKHz/24 bit DACs, which are also on the 2500.
The 2500 is more of a re-design and most of the new features are not in the 1500. The 2500 includes a new GUI for the OSD, although it appears to be mostly a visual enhancement to the setup on the 2400. The GUI is not included on the 1500. The front panel has the same new look at the 1500, but the rear panel has been re-arranged, with the addition of a third set of component inputs and a new speaker terminal wrench! The 2500 has the new remote, with the addition of 2 keys to recall saved settings, which are set as part of the GUI. These appear to be the same home bank save/recall features that were available on the 1500/2400 - they are just now in the setup and on the remote. This allows saving and recalling different YPAO settings, amongst other things. The save/recall volume discretes are still present on both the 1500 and 2500 but are not available on the remote. The 2500 also lets you trim the inputs to account for different levels on inputs from various devices. This is a great addition, but the 1500 does not have this feature as far as I can tell.
PLIIx Movie and Music discretes are included in the 2500, but are not available from the remote and are not available on the 1500. It is nice to have these included in the extended IR codes, but it is very disappointing that they are not directly available on the remote and that they seem to be excluded for the 1500. Given that these discretes are available on the 750, it really disappointing not to have them on the 1500. The 1400/2400 were one of the very first PLIIx implementations, but the access to those modes was very hard to learn. It looks like it is only marginally better for the 1500/2500, which is disappointing.
The 1400/2400 seemed to be basically the same designs, with some additional features on the 2400 (RS-232, zone 2 video out, different remote, and slightly more power). The addition of new basic features (like the GUI setup, the PLIIx discretes, input trim, 3 component inputs) seems to indicate a bigger difference in the design of the 1500 and the 2500 than in the previous units. The really new features (other than the new DACs) seem to be only on the 2500. One question that I have is whether the YPAO was improved on the 2500 and if so was it also done on the 1500. That I cannot tell from the manual, unfortunately.
The 1500 looks like a combination of the old 1400 and 2400 with some minor improvements. Compared to the 1400, it has more power (like the 2400), an RS-232 interface (like the 2400), a new front panel display (volume in dB rather than a bar graph, PLIIx light added and some minor re-arranging), the RS-232 portfrom the 2400 has been added to the rear panel (which otherwise looks like a 1400), and it has a new remote. The remote includes macro capabilities as well as the ability to access "optional" discrete functions like the 2400 remote could, but which was not available on the 1400 remote. Audio delay/lip sync is still not on the remote. If you look at the new RS-232 control codes, they even reference the 2400 in one place, making it pretty clear that the 1500 is mostly a mix of the 1400 and 2400. Additionally, the lack of the new PLIIx discrete extended IR codes (available on both the 750 and the 2500) and input trim - see below - supports that conclusion. The 1500 does have new 19kKHz/24 bit DACs, which are also on the 2500.
The 2500 is more of a re-design and most of the new features are not in the 1500. The 2500 includes a new GUI for the OSD, although it appears to be mostly a visual enhancement to the setup on the 2400. The GUI is not included on the 1500. The front panel has the same new look at the 1500, but the rear panel has been re-arranged, with the addition of a third set of component inputs and a new speaker terminal wrench! The 2500 has the new remote, with the addition of 2 keys to recall saved settings, which are set as part of the GUI. These appear to be the same home bank save/recall features that were available on the 1500/2400 - they are just now in the setup and on the remote. This allows saving and recalling different YPAO settings, amongst other things. The save/recall volume discretes are still present on both the 1500 and 2500 but are not available on the remote. The 2500 also lets you trim the inputs to account for different levels on inputs from various devices. This is a great addition, but the 1500 does not have this feature as far as I can tell.
PLIIx Movie and Music discretes are included in the 2500, but are not available from the remote and are not available on the 1500. It is nice to have these included in the extended IR codes, but it is very disappointing that they are not directly available on the remote and that they seem to be excluded for the 1500. Given that these discretes are available on the 750, it really disappointing not to have them on the 1500. The 1400/2400 were one of the very first PLIIx implementations, but the access to those modes was very hard to learn. It looks like it is only marginally better for the 1500/2500, which is disappointing.
The 1400/2400 seemed to be basically the same designs, with some additional features on the 2400 (RS-232, zone 2 video out, different remote, and slightly more power). The addition of new basic features (like the GUI setup, the PLIIx discretes, input trim, 3 component inputs) seems to indicate a bigger difference in the design of the 1500 and the 2500 than in the previous units. The really new features (other than the new DACs) seem to be only on the 2500. One question that I have is whether the YPAO was improved on the 2500 and if so was it also done on the 1500. That I cannot tell from the manual, unfortunately.
