Idog,
I passed on the 300s - I guess I came here to be talked out of them, and it worked (my wife thanks you all...).
I am currently using a Pass Labs X250 amp and X1 preamp. I think they sound pretty good - had a Threshold T200 previously, which I thought sounded very good, too - a tad warmer.
I have heard that Genesis work best with tube equipment (I think Arnie voiced them on tube stuff) but I have always been a fan of good SS. I am a musician and like to hear a LOT of sound. I have read reviews on the X250 saying that the blue meter hardly moves even at high listening levels - I can get mine to swing wildly back and forth :-).
I have not heard the new 501s, so I can't comment. I'm sure there good. I have heard people comment they prefered the V to the 500 and 501, but this is secondhand.
Jim