<font color='#000000'>Brent;
If I may offer my 2cents here for what its worth.
The Yamaha is absolutely stellar as a home theater AV Receiver in 7 channel. The added front effects channels are truly missed since I sent it back to Yamaha. However, most of the DSP modes are not ideal for music listening and I actually preferred prologic II and DTS Neo modes in most cases. The RXZ1 will serve most home theater needs quite well.
However, the B&K AVR507 has advantages:
1) Adjustable crossover settings (Essential in my application)
2) A more meaty amplifier section
IF you are running full range speakers in the front, in a reasonably large room with preference to music over movies and have no future plans to add additional amps, I would recommend the B&K AVR 507. Conversely, if you are running all small speakers and listen to more home theater than music, I would lean towards the Yamaha RX-Z1. Both are excellent units with their own associated strengths and weaknesses.
I would suggest doing demos of both at a local hifi shop to see how you like the user interfaces of each as well.
Also, don't forget the RXZ1 sells for over $1000 less than the B&K AVR507 which speaks volumes for the RXZ1 that it could even compete.
At the $4K range, you may also wish to consider the Denon AVR-5803. I am currently reviewing this receiver and loooooooooove it! The user interface is challenging however, but the fidelity is superb.
Hope this doesn't confuse you more than help.
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