Seems that you can't find anyone that has experience with both. I haven't heard the Benchmark, but had a Bel Canto DAC1 a couple of years ago and was not impressed.(even though I like Bel Canto in general) I have owned the 840 for about a year and find it to be excellent, more like a $2-3k player.
I believe that it actually has 2 of the Wolfson dac's, one for each channel.
I use it w/ a tube amp and it is transparent, detailed and musical. Not certain that it would mate as well w/ a SS amp that leans toward brightness. If you buy used, I would imagine that either the 840 or the Benchmark could be resold w/ no problem.