Well my budget for an amp is ~$400 at most. I'm looking for an amp in that price range that complements the HD650 and is much much better than the NFB-12 amp. I mean I paid $250 for the NFB12, so I'd expect paying $200-$400 for a dedicated amp should be a huge upgrade. Even better would be a DAC/Amp combo in which case I could sell the NFB-12.
I suppose the NFB-10se was a pretty good option I was told about (over $400, but justifiable since it has a DAC and I could sell my NFB12), but I sometimes get the impression people recommend DAC/Amps just for the DAC and assume you have some esoteric $10,000,000 vintage tube amplifier with magic tube pixie dust and power line conditioners. Is the NFB-10se amp truly a great SS amp for the HD650 (I would not be using it balanced most likely)? And if not, what else are my options in the ~$400 range for amps or $500-$600 for DAC/Amps?
Generally SS amps tend to sound quite close, so it might be a good idea to start by tempering your expectations. Now $400 is an odd price range, my best recommendation would be to find an M3 or a used Burson. I'm not sure how much it is to have an M3 commissioned if you're not into used products.
Have you ever seen Milosz' thread A/Bing amps? Go find that, helps temper expectations.
The Burson does have a weird reputation (apparently it's "musical", whatever that means. An amp can have good dynamics but musical? Does that mean it's funky? I'm not into investing hundreds of dollars for a funky sound [but YMMV].).
I can't really comment on the HD650s with the NFB-10SE as I've never heard both together, but have only heard them separately. My impression of the NFB-10SE is that it's a dry sounding thing. Very androgynous. From what olor1n has posted of the two together I gather that the 10SE manages to take away the one thing the HD650s really have going for them: the ability to engage & move the listener. But it is apparently quite resolving; which works out well if most of your music is from Linn, Chesky, HDtracks, 24/96, 24/192, 32/384, etc. etc. etc.
In the higher end: I know the Beta22 sounds GREAT. I've tried the V200 and I would take a 2CH. Beta22 over that. Haven't heard the HD650 and Beta22 together but hoping to in January.