Krell MDA 500 vs KAS vs KAS 2 vs 750Mcx vs 450Mcx

Looking to potentially upgrade my MDA 500. Does anyone have experience in relative sound quality for the Krell amps identified above? Thanks
I once owned the MD-3oo's.Fine sound,but too hot running.I did hear the KAS -1 running the mid tweeter panels of an Infinity IRS-2 set-up a while ago,and that system changed the way I listened to music "in the home environment".I had brought along A Harmonia Mundi analog pressing called Ancient Dances of Hungry,the sound of hall was captured incredibly well as was the correct timbres and harmonic structure of the music.A GREAT system,but,could not perform to that level without such a GREAT amp as well.Good luck!
Had the KSA 250's, 750McX, a lot of exposure to the 300 MDA some 500s and some 350's as well as 650's and a lot of time logged with owning the FPB 600. I'd say that the the sound of the 750's is less gray, far far less grainy, more textured, faster, more transparent, detailed and able to carry off tone and color quite a bit better than the older series KSA with much less of that slightly mechanical, grey slightly darker quality. The newer series may not have as much depth and 3 dimensional imaging as the 500's. The 750's are in a different realm when it comes to uncompressed unrestrained dynamics, as good as the 500's are, and are more transparently neutral with less of a sonic signature over extended listening, getting out of the way of the music and disappearing.
I am a former MDA 500 owner. My signal path was KCD to KSP64x upgraded to KRC3 preamp to twin MDA500s via balanced Rhapsody cables into two Thiel CS5is. The sound was STUNNING for the 7 years that I owned it. I also have auditioned the KAS and KAS2...the MDA500 are/were brute, pure control over the woofer/subwoofer panels. Intense sound with unbridled power and immediacy like no other amps I have heard. These outperformed the KSA-250's as well. The heat generated at idle or partial gain was deadly! I had to replace all electrolytic caps* in preamp, amps, and KSP because the heat dried them out. $600 bucks! I miss the sound though. Very much. *(Not the massive filter caps though) Good listening!