I find a preamp makes a big difference in all the systems I have put together. And IME volume control on a DAC doesn't give the same sort of dynamics, ooh and impact as an active pre (I have found these things lacking on passive preamps as well).
I run a dB Audio Tranquility with my VR-4 Gen IIs, but I wasn't making my DAC choices with these speakers.
As with most things, I recommend auditioning if at all possible. Narrow down your choices on forums like this one an then try to take a listen (in your system if at all possible). At the under $2000 price points that I know best, here are DACs I would try to listen to:
Antelope Zodiac
wyred4sound DAC2 or DAC1
Eastern Electric DAC
dB Audio Tranquility
I have heard all of them and they all sounded great. Just different flavors (which reviews of them capture nicely). If I were going to change up DACs personally. I would probably try the Zodiac first.
Also, I would agree that the Benchmark is getting a little long in the tooth. IMO, DACs are the segment of the audio market changing the quickest. You often read about newer DACs offering quality digital sound not possible at such low price points 5 years earlier.
Lastly, don't just get enamored with DAC chips alone. Power supplies an analog output stages matter a lot still (as with most audio electronics).