Audition gear your own home with your ML speakers...
Neo,
Welcome to the ML Club!
The speakers you have choosen are excellent ML speakers. I would have to agree with others here though, that the, ML Grotto may be, a bit small given your room size. I would highly recommend the, ML Descent. It is a truly powerful servo subwoofer, but if money is an issue, I would recommend the, ML Dept.
IMHO, I did not like the B&K 507 AVR, and I'll tell you why...., IMHO, it was just too bright and brassy, also it was just did not have enough current - ampheres. ML speakers really need lots of power. ML speakers can and do go down to 1 ohm or less, espeically, in HT with loud dynamic effects... I would recommend seporates with a powerful amplifier i. e., Anthem - A2 or P2 and/or A5 or P5, Cary Audio -'Cinima X', Sim Audio's 'Moon Aurora'. I recommend Anthem's D1 or D2 processors. You might try Sunfire (Digital) amps and processors.
Listen first, then try to audition the amp.'s and processor equipment in your HT. The key to finding, what sounds good in your own environment..., is to take it home, and audition it there. Try out the amplifiers and processors first, on your ML speakers, at home, before you lay out a lot of money.
Remember to, "Trust your ears".
Enjoy, and Welcome!
Cheers
-Robin