Big mistake. The m900/c900 was so much better than the 509x on the same system. I ended up staying about an hour + listening to that combo and tossed out the idea of the 509x. The m900u has much more power than the 509x. It was easily demonstrated on the TAD ME-1 monitor speakers that were hooked up to the system.
I did not get the m900u/c900u combo because I found something more appropriate for my smaller space. However, I may revisit the Luxman amp in the future for the bigger space downstairs. I will not get the C900u preamp since I will use a Benchmark HPA4 preamp from now on any system I build.
BTW - I had about a 3.5 hour drive home because I stayed longer to demo the m900/c900 combo. It should have been under 2 hours.