They are somewhat the same, but the M-500 has a couple of quirks. There's those little boxed daughter boards (two of them IIRC). One is the phase network and the other is the voltage regulator (both in the power supply). Nothing in the phase network of concern, but the voltage regulator has a bunch of caps in there. See below. Both boards were eliminated on the M-500t (parts became part of the mother board). There are some other parts on the M-500 that are missing on the M-500t, like the inductors on the amplifier board, and a network that may or not be there, based on the particular build of the M-500 that you have.
Here's the voltage regulator daughter board that was a real pain to work on. It is soldered to the mother board on risers that are also conductors.
It should sound like it isn't there!
There is a difference between hearing and listening...
Making life enjoyable through expensive electronics.
Carver: C-4000 & C-1 preamps, PSC-60 preamp/tuner, TX-11a tuner, M-400 (2), C-500, M-500, M-500t, M-500t Mk.II, A-500x, AL-III loudspeakers (2 pr.)
Sunfire:Theater Grand III processor, Ultimate Receiver, Cinema Grand Signature 400 ~ seven, True Subwoofer Mk. II, D-10 Subwoofer