The 250P is the Krell item that was actually somewhat in-between the older Krell sound and the newer "bright/forward" Krell sound. The 250P had good resolution and definition, but had just a tiny bit of warmth there as well. If you’re really worried about this, maybe look for a Krell KRC-3 (it still has a home theater passthrough). The KRC series is older than KAV-250p and a bit warmer, but sometimes you can hear sibilance in vocals and a tiny bit of smear (from the warmth). I would avoid the Showcase / HTS7.1 / KAV-280p if you don’t want the forward/bright sound.
The 280p pushed for resolution and clarity and strength in signal. This is actually what I love because the resolution reveals more realistic sounds. Though, you will want to make sure you stay away from silver interconnects and speaker cables.
The older Classe preamps (like CP45 / CP60) were VERY VERY warm and slow. (way too warm/slow for me). I think the newer stuff is not as warm. I’ve read descriptions of the newer Classe as being very smooth, silky, liquidy (maybe the SSP-300 would have some of this).
I don’t know what the Simaudio / Parasound stuff sounds like.
Like gregkohanmim has said, you could really use any preamp here. If it doesn’t have a home-theater passthrough, you would have to reset the volume to a specific level every time you use the signals from the Yamaha. (maybe set at 50% / 75% / or a specific number on the preamp display).