"Double" bi-amping a good idea?

You don't have to use an external crossover if the speakers are set up for bi-amping. The sound will be better with the external crossover but since good ones aren't cheap, I would just plug 'em in and use the passive crossover in your speakers instead and later figure out if you want to go active!

I also think that for the costs of four amplifiers and two sets of speaker cables you would be better off selling your amps, combine that money with the money for the second set of amps, and buy yourself one great amp.

Power is important but the quality of parts are even more important. I would buy the best amp you can and then down the road on your next upgrade buy a second one.

My suggestion, would be to definitely bi-amp. Then when you can afford it, purchase an external electronic crossover to actively bi-amp the speakers.
As "Mgottlieb" mentioned, I have had the B&W800's for years and just recently actively bi-amped them (with Krell amps and crossover). It was the biggest improvement that I have ever made to my system!
Richard

Tekunda,

I never said that you needed an external active crossover to bi-amp. You can just use the passive crossovers in your speakers. Going to the vertical bi-amp configuration should improve your sound noticeably without you having to buy anything else.

Later, down the road if you feel you want to go to an active external crossover you can always do that and it will likely improve the sound even more. You can get a decent active crossover used for under $500. The hardest thing will probably be taking your speakers apart to disconnect the passive internal crossovers (lethal voltages may need to be discharged too) but the folks at Martin Logan would be able to advise you of just what is involved to accomplish that. They could also advise you as to what crossover frequency and slopes to use. It could be a fairly simple, straight-forward operation, so it wouldn't hurt to give them a call just so you'd have a complete view of all your options (before you rush out and buy the crossover and then find out that it's not a job you'd care to tackle). Happy listening!

Tek you might as well try the vertical passive biamping: it sounds like you're presently bridging the stereo amps, which halves their damping factors resulting in degraded control of the speakers by the amps.