Details for bi-amping

I am concerned that unless you have 4 exact amps, and 2 exact stereo preamps, the sound may be difficult to meld inaudibly.
Its not just a matter of gain matching at a particular frequency, but to track all the sound at any frequency exactly right....and too the dynamics have to be the same or the system will sound different at different sound pressures. If you listen to classical music or jazz at all, this would be of great concern.

Wow, what a bunch of nonreading and confused writing.

The OP first writes that he wants to use tubed amps on the top and SS amps on the bottom; later he writes that he wants to use indentical amps. Which is it? Tubed and SS or 4 identical amps? I suspect it's the former.

One preamps will do, and in fact the use of 2 preamps will complicate matters substantially. Y-connectors work just finely and are almost free. After you decide if you want to continue your experimant, you might look for a higher-resolution solution.

Stanwal is correct that you'll need some way to reduce the Voltage gain (NOT 'sensitivity') of the higher-gain amp(s). Of course, the easiest way to do that is to turn down the level of the higher-gain amp. However most poweramps don't have gain controls, so you'll be stuck having to use the passive attenuators that Ngjockey mentioned.

Good luck. I suspect that you'll decide that it's more trouble than it's worth.
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Sorry fot the misspellings; too bad this forum chooses not to have an Edit feature.
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The sensitivity of an amp is how much voltage it requires to drive it to full output. For example my Meridian 605s require .5 volt for full output; my CJ 350 takes 2 volts. Since the tweeters will take much less power to drive than the bass section it will probably , but not certainly, be the tubes that need the volume control or attenuation.

JeffreyBehr, I think he means that he wants to use a pair of monoblock solid state amps for the lows, and a pair of monoblock tube amps for the mids/highs.

You are of course making a good point that what needs to be matched is gains, not sensitivities. More likely than not the solid state amps, presumably being more powerful, will have higher gain, and therefore their inputs will probably be the ones having to be attenuated.

I second the comments about biamping being more complex an undertaking than is often anticipated, with there being a substantial possibility of disappointing results.

One of the most common misconceptions about passive biamping (i.e., biamping without an active line-level crossover) is that it makes sense to use a powerful solid state amp on the bottom, and a much less powerful tube amp on top. In addition to the possibility of that resulting in a sonic mismatch, what is commonly not realized is that much of the power capability of the solid state amp will not be utilizable, because how much of its power capability can be utilized will be limited by the clipping point of the lower powered amp. In a passive biamp arrangement, the mid/hi amp(s) have to output just as large a voltage swing as the bass amp(s).

Regards,
-- Al