That is, of course, a tough question to answer.
It will be difficult to improve on the sound quality of your B&K receiver that you now have. The NAD receiver (which I have not heard), may be about as good in build quality, and roughly as powerful as what you now own. I doubt if it will be noticeably better sounding. It will however give you the HDMI connections you want.
For $2,000 or less, I'm hard pressed to give you a better suggestion. If it were my choice, I'd keep what you now have.
For what it may be worth, Outlaw has a new pre/pro in the works,
the Model 997, and they say it will sell for $1400. You will then have to find a 5 channel amp, but you can find good used amps at Audiogon. I have seen B&K 5 channel amps similar in power to your 305 receiver (125 wpc at 8 ohms) selling for roughly $500. If you want more power, I'd go for at least 200 wpc at 8 ohms. You might also be able to sell your 305 receiver for $400-500 on Audiogon.
Is your first priority the HDMI connections, or is it improved sound quality?