Hi

I believe if Line6Hugo has stated this (and I did see the post previously) that it is true as he will almost certainly have confirmed this with the CS team and the product development team.  You can check this yourself by: a) recording a clip from the standard outputs with the output mode set to Stack Pwr Amp amd then; b) in Combo Pwr Amp mode but with the Cab/Mic model for the same patch disabled,.  The sound you get should be the same in both recordings

There are two sets of amp models FULL and PRE specifically because the PRE models are designed to work with the DT50 whilst the FULL models are designed to work with other amplification systems where the HDx00 is not able to adjust the physical output characteristics of the power amplifier in the same way as it can with the DT50.  You will probably find that if your amp is a Class A/B type, the PRE amp models designed to work with Class A/B power amps might sound better and similarly if your amp is a Class a type amp the Class A PRE models might sound better.

These are only guidelines.  There are no hard and fast rules, so the 'what your ears detemine sounds best for you' statement is perfectly acceptable.  Some users do feel that the PRE models work better for them in some cases.  It's subjective and very dependent on the type of amplifier you are plugging your HDx00 into - and as you know not all amplifiers are created equal.

Nick