I have one of each. The 5040 says Sonic Blue and I purchased from DNNA refurb'd. The 5540 I bought new.
There's no difference in the two units what-so-ever. The amount of fan noise is negligible for both.
If you have cable or sat, the existing DNNA guide data works fine. If you are OTA (like me), then you can use WiRNS to either remap a cable lineup to meet your needs, or use WiRNS with Schedules Direct.
Technically, the 55xx units have CA and IVS disabled. However, that is easily remedied and (AFAIK) most folks with 55xx units have these enabled.Warning: Spoiler! (Click to show)
Up until the very last software version, they were easily enabled via a "mothership proxy", such as provided by WiRNS. The last official software version (5.1 v144) made that trick not work. The fix to that is to revert the software to an earlier version
, and use WiRNS to re-enable the features and prevent software updates.
(Thus the only advantage of the 5040 over the 5540 is that you get CA and IVS without needing to do anything)Edited by jlv - 8/25/12 at 11:35am