"Double" bi-amping a good idea?

I'm not familiar with Martin Logan crossovers, but you may well need to remove all or certain components of your speakers' internal crossover if you go to "active biamping" with an external crossover. Check with the manufacturer and see what they advise.

Good luck ... I haven't done this myself yet, but if you use a good external crossover "active bi-amping is supposed to be an terrific way to go . BIG gains in clarity and effective power from your existing amps.

You are right. I am not bi-amping, but monoblocking right now.
But why must I use an external cross-over when trying your vertical bi-amping suggestion? Could't I use the internal speaker cross over in my speakers, like Martin Logan suggests?
And since I bi-wire my speakers anyway, I would not have to invest in extra speaker cabling.

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