Furman X-312 - a good subwoofer crossover?

I don't know much about the Furman, but it seems designed for studio use.
I'm using a Paradigm X-30, which is great value and does the trick. I had the same question as you, but was reminded -- this is a subwoofer. I bought mine used from Stereo Trading Outlet for $120. He's got one now on audiogon for the same price.
If you wanted a little bit better, I think Hsu Research has one for about $400. Try Jeff's Sound Values.
And, if you really want to go nuts, there's the Bryston 10B, $1400 new, but I think that is WAY overkill for what you want.
For my money, the Paradigm is the ticket.

dunno about the furman, but the marchand xm-9 w/upgraded op-amps, is at least as good as the bryston, at less than half the price. and, w/24db/octave slopes, & w/its wolume pot at the chosen x-over frequency as well as for low & hi-pass, it's ultimately more flexible as well...

doug s.