geowak,
I've owned my B60 for about a year and a half and couldn't be happier. I honestly haven't found any shortcomings yet. Its pretty difficult to describe it, but I'll try my best...
Its neither forward nor laid back. Its not bright nor warm. Its very transparent, clean, and dead quiet. Its not a smooth, liquid sounding amp, but its not in your face, harsh, and aggressive either. It just gets out of the way and presents the music, nothing more or less. Despite being detailed and faithful to the recording, its very musical. It'll show you what everything connected to it does.
Its a true dual mono amp - 1 power supply for each channel. Its built rock solid and has a 20 year transferable warranty. Look at the "Any internal pictures B60" thread I started in the Bryston Circle a while back (page 11). They have options for remote, MM phono stage (I use an MC Dynavector 10x5 with no problems), and an internal DAC. If you need a phono stage or DAC, Bryston can retro fit them (not both - not enough room). Not sure about the remote though.
Downfalls?
Its only 60 watts. They're a very strong and dynamic 60 watts, but 60 none the less. If your speakers are power hungry and want rock concert levels in a big room, look elsewhere. If you keep things under control and don't expect it to do what its not designed to do, you won't have any problems. Its very capable of driving my Yaras to levels far louder than I care for in my medium sized room.
Some have called Bryston dry, clinical, bright, warm, dull, and everything else in the book. They're correct in a way. Bryston will amplify exactly what its given. I haven't heard the Benchmark, so I can't comment on it. I've read a bunch about it though. Its sounds like what Bryston is all about. Will it be too much of a good thing? Not sure. If you're looking for something to warm it up, smooth it over, make it fuller, you're not going to get it with anything Bryston. That's a double edged sword some times. However, I have heard a ton of Bryston amplification, and I think the B60 is the sweetest sounding of the bunch. Not overly so though.
I can say that it sounds awesome with the Apollo. It gets every last bit of what the Apollo offers. A better source will be better. I'm currently saving up for a Bryston BDA-1 DAC.
I'm curious about the Benchmark. How does it compare to the Apollo's analog output?