5.1 DTS CORE with OPTICAL cable ???

Yes. But that won't help with a 5.1 PCM track. It's a great disc and the stereo track will be fine over optical.

Correct. DTS core is only available when the soundtrack is encoded using dts-MA.

As with many concert 5.1 mixes, the surrounds are mostly ambience. So, playing the stereo track and applying a surround mode like PLII will give you much the same experience as the PCM 5.1 version. Or, if your player offers a surround encoding option when downmixing the 5.1 version, then using PLII in the receiver will give you an output that is quite close to the 5.1 original.

No, on Blu-ray, Dolby Digital and Dolby TrueHD are kept separate. The Dolby Digital track can go over optical, though.

Yes, sort of. It's a companion DD 5.1 track that's embedded in the TrueHD package. Dolby and DTS use different techniques with their lossless encoding. But, the end result is the same - a high bitrate lossy output that gets sent over optical and digital coax connections.

Yes. 640 on BD. DVD maxes out at 448 and is often less.