Bridge or bi-amp? Which should I do?

The issue of good sound is always a quest. For this reason, the audiophile is engaged in an activity not unlike that of a dog trying to bite its tail. Never ends.

My dear friend, why bother? Those components of yours will not take you far. Harshness, harmonic artifacts, lack of proper soundstage and sheer frustration will be sitting next to you in your listening room. Simplicity is of utmost importance regarding your issue. Integrated is simply not the way. Even in hoods this is a well known fact among the rappers. Why, then, do you even bother to complicate your life? Listen and learn, listen and be wise; now you won't be able to sell your gear even in the hood...

An old classic tube receiver, some loaded horn speakers and a good self powered sub will save you headaches. Will beat the crap out of what you have. Just post this thread in Audioasylum and wait for the fish to bite.

Listen and be wise...

I may be dense (may?) but, how are you intending to do this bi-amping? Do the high-level outputs on the C370 stay active when using the pre-outs? Or does it have main-ins, and you are going to use a Y-splitter off the pre-outs? And if either is true, does the amp have adjustable gain so you can match properly? Doesn't bridging or bi-amping with non-identical amops introduce all manner of potential to screw up something?

I decided to bridge my amps and love the results. Big, open sound, huge soundstage.

Pretty sure they do, as I tested them prior to this response.

NAD amps can be bridged, but when I did so with my 3400 and 2400 amps (sister products) to rum my Mission 765's, there was a very definite decline in the sound quality. The trade-off to maximizing power output(and there is always a trade-off) is the sound output took on a much harder edge. Bi-amping preserves all of the sonic/headroom benefits with absolutely none of the trade-offs.
In your case, I would have used one of the amps (the one with independent level control) for the HF and the other for the low; or the more powerful amp for the LF.