What can I expect, if anything going from a ma6500

D100 functions as either a pre-amp or DAC-only, so no problem going direct to the MC302. It also offers balanced outputs, a big plus going to a separate amplifier and improves the S/N ratio on the MC302 quite a bit. Only drawback is that D100 has no analog inputs at all, so no legacy gear. Regardless, you will very likely hear a big improvement over the DAC-to-integrated method you are using now. Simpler circuits are usually better.

MC302 versus MC452? Very big difference in money for only 1.5 dB increase in output. Audible, but worth it? Only you can decide. I love my 302; plenty of power, control and silent depth for my needs.

Have fun and happy listening!

I'm pretty sure your dac has its own volume control. If that's the case, I think you'll have a very nice upgrade going to the mc302. For 2 reasons. First, the 302 is probably a more powerful and a better sounding amp. Second, and more importantly, you won't be going through the preamp in your integrated. That's a very big difference. Opinions vary, but I feel that if you don't have a truly exceptional line stage, going directly to your amp from the dac is the best way to do it.