Greetings. I actually have one of these Onkyo M-510's and love it. First, I will confirm the obvious. The 510 is extremely powerful, dynamic, very clean, and presents well. I have been running it with an Audio Research LS2B preamp, and a Marantz SA-11S1 super audio cd player. I have pushed the Paradigm Studio 100's, JBL 240ti's, and Sonus Faber Concerto's with it. All of them sounded great. Definitely very tight and fast bass, and deep. This amp will not run out of power too easily.
I do not agree with people that have or have had 1 or 2 "expensive audiophile" amps in their lives, passing judgement/knocking against such an impressive machine, without ever hearing it. Onkyo only made a few of these, as their flagship taunting, and they are loaded with very serious hardware.
Bottom line, this is an awesome amp, capable of running in different circles and coming up respectable. Lastly, has anyone seen the resale value of a Krell or a Mark Levinson amp, 10-20 years later ? Funny, but I always see them selling for about 1/2 (half) of the original list price, and often taking weeks to sell. This would "Never" happen with a Grand Integra. Food for thought. Peace out.