I want to upgrade to a bi-amp setup.

You can mix it up, as you state it. Use the 2500 for 'bass' and the premier on the high end. I bi-amp a c-j premier 11 tube amp along with a c-j mf2250 into my kef ref. 3-2 speakers. I have two sets of connectors at the back of the speakers to run seperate cables to. Be sure to remove the 'jumper bar' connecting the two together, if your b&w's have a similar set up. Remember, one set of cables from the premier to the high end, one set of cables from the mf to the low end. This is true bi-amping. Also, you will need two sets of cables connecting from your pre-amp to each amp, or may require a spliter jack.
Regards,

Don't bother using two amps unless you also use an electronic crossover.

Unless you use an electronic crossover that provides multiple outputs to multiple amplifiers all you accomplish is additional power. Is that what is needed?

If so, then the issue for not idential amps is Gain. If one amp has a gain of say 26dbl, and the other 30dbl, then you lose seamlessness of integration of frequency range of the different drivers.

If say the 30dbl gain amp is connected to the tweeters then you have essentially 'turned up' the treble, or vise versa, if you see what I mean.

If you do need more watts of power to drive your speakers and you have an extra amp (with the same gain) you want to use instead of upgrading to an amp with appropriate power, then intall a splitter cable between the preamp and the amp. Then one spker cable to treble, and the other to bass.

You now have four amps driving your speakers instead of (stereo) two. Add up the watts and especially be careful its not too much even if the one amp is below, or close to the minimum specified by the mfgr. You can contact them to find out the power recommendation if not in the manual.

You an see its a lot of trouble and expense if you do not need more power, and nothing is really gained if you do not.

I am currently biamping my Magnepan 3.5s with a tube amp for the midrange/treble (ARC VT100 mkII) and solid state for the bass panels (Kenwood LO7M monos). I am using a Marchand electonic tube xover (Marchand XM126). I am very happy with the results. The Marchand allows multiple xover points and symmetrical/asymmetrical slopes. The levels can also be varied continuouly. This flexibility facilitates seamless blending of the drivers. In addition, the Marchand xover has not introduced any noticeable grain or electronic artifacts. The presentation is seamless, transparent, delicate, dynamic and musical with a huge coherent soundstage.
The marchand XM126 is highly recommended.

Concerning the amp, itself: Bryston has great specs (though pricy) and is comparable to Muse 160, ATI, or even the vintage Hafler DH-200/220 amps. Or, remember the BEL 1001? I have not seen on the market lately.

Jeff Rowland makes accurate amps too, but man,they are works of art. You can take off the cover and hang it on wall. Really. It comes with an optional clear plastic cover to reveal its awesome interior. But $8k !? for no better actual performance than the $200 Haflers?

ATI is probably the best price/build quality value. But either will do your speakers justice.

You cannot do better than the entire B&W line for enclosed cabinet (box) speakers. The only upward mobility toward 'true to the original', is dipole: ELS, planer/ribbon, or open baffle designs. See www.linkwitzlab.com

Once you get there, top end components, cables, or tweaks become inconsequential. You are finally free of all that nit-picking futile nonsense. You are immersed in enjoying the music. Since you can finally hear it. Though you have also become selective in what is in your collection of source material, since you can accurately hear it, and its typically lousey to mediocre sonic characteristics. But when you find well engineered, sparingly mixed, sonically superior recordings, and close your eyes... you are there. Or they are here, whichever :-)