The problem is probably the output stage on the Buffalo versus the zapfilter. I assume the Buffalo you are talking about was using the Ivy output stage? The one I am listening to is certainly not deficient in bass, but also is not a bass monster or whatever. It is pretty equivalent in the low end to the rbroer I/V stage in my Rotel, which is DC coupled and is quite neutral (no caps, etc. in the signal path, so nothing other than mf resistors and the Toshiba 2SA970/2SC2240 transistors to color it).
It is also a possibility that the zapfilter is overblown in the bass Dunno, never listened to one, and think they are overpriced.