Todd,
I haven't compared the Pioneer or the NAD but I have heard the HK's (although I don't think they have an 1804 model) and ended up with the Denon AVR-1804. The HK at the same price point has a lot less power. Right now on Cructchfield.com the Denon is on sale for $399 which makes me cry because I bought mine only a month ago for $499. Anyway, it is a wonderful receiver... 6.1, 90 watts of very clean power per channel... the whole array of Dolby and DTS compatiblility, but most importantly to me, just like you, it sounds wonderful with music. The treble and bass can be set independantly and it is an easy to use and intuitive receiver. I listened extensively to the Yamaha's and the Denons and finally decided Denon based on build quality... frankly they are both excellent sounding amp's. I hope this gives you something else to consider.
