Horizontal Bi-Amping question

I have an ADCOM 5400 2ch amp (125W x2). and a Marantz MM9000 5ch. amp(150W x5). and I want to bi-amp my two main speakers using two of the 5 channels on the Marantz and the ADCOM. My question is which amp should I use for the hi,mid freq. and which should I use for the low freq.?

I suspect that the Marantz should power the lows and the ADCOM should power the hi and mid? The other option is to forget the bi-amp deal all together and just use the ADCOM for everything. I'm mostly concerned about the best possible sound for music.
I personally would use either the Adcom by itself or 4 of the 5 channels of the Marantz for bi-amping your speakers. I would not mix the two amps on the same pair of speakers for several reasons.
1) Each amplifier has a sonic signature. Chances are that if you mix these components, it may not sound proper.
2) Depending on the speaker, I have seen the grounds tied together on the crossover. This has the potential to create a ground loop in your system (making a higher noise floor).
3) If this is a HT setup, the 5th channel will be the same sonic signature you may use for the center. The Adcom could be used for the rears.

I would experiment and see what works for you...
Best of Luck!!
J_k advice is good. But since you already have the amps, why not just do a listening test yourself and determine what sounds best to you. Sometimes different amps can be a benefit. In my system I'm using Krell on the bottom and Levinson on the top. I don't much care for the Krell on the top, it's too harsh. I like it on the bottom end--it has more control in the lower octaves than my Levinson. Most poeple will agree that matched amps are the easiest and least problematic way to go for bi-amping. If you were planning a purchase I would give the same advice--but since you already own the amps--why not just test it yourself?
I am assuming that you are passively bi-amping (whereas I am actively bi-amping), so take my advice for what it is worth.
I partially agree with "abstract7", but I do use different Krells for both highs and lows.
I had first listened to which amp I thought gave the best overall sound, and then used that for the mid/highs and the other for the bass. The result is fantastic!
So, LISTEN, and make the decision based on that.
A simple test to see if the highs and lows are tied together via using a common ground in the crossover would be to disconnect the shorting strap and then check for continuity between the two ground posts. If there is continuity, bi-wiring would be fine but i would not bi-amp.

Something else to think about when bi-amping is the "time delay" factor of the various amplifiers involved. Due to different "lengths" of the internal circuitry of different amp designs, the signal could come out of one amp slighty ahead or behind the signal from the other amp. This would surely affect the perceived "prat" of the system along with dynamics. Since most manufacturers don't even give this spec, it would strictly be a crapshoot as to whether or not two different amps would work out "cohesively". The only way to get around this "problem" would be to use two identical amplifiers. Sean