First of all, I'm very happy with the general sound of my setup, but would like a little extra punch. Do any of you have a recommendation for an amp? If I buy one, how many channels should it have and watts? I'm looking to spend less than $1000 if possible. Thanks for in advance for the advice!

Here my setup:
Onkyo SR875 (140w x 7)
Fronts: JBL S412PII (Timbre is very close to Axiom VP150)
Center: Axiom VP150
Surrounds: 4 x Axiom QS8

Please expand on what your mean by "punch"? That receiver has more than enough power to play at extreme loud levels. Are you talking about more bass? If so, a sub might help.

Sorry, I'll expand on my meaning. Each front has a 200w sub built into it, so bass is really not the problem. I guess I'm just looking for a more dynamic soundscape. Maybe I just need to tweak some levels in my receiver? Would an amp do anything for me?

Harp, welcome. Yes, depending on what you mean by "punch", you may be in need of main speaker or subwoofer advice, but it's highly unlikely that you need amplifier advice. Your 875 has plenty of power to play those speakers at levels that won't damage your hearing , or even a bit more. You may be looking at the least likely suspect to solve your case.

A "more dynamic soundscape" comes from the source material, not the equipment.

I would start looking for a different set of main speakers for added punch. Quite often the "punch" people are looking for is from the mains themselves and with the built in subs I suspect much of the punch is lost through the mains. Just remember your room and/or seating position could also be killing/missing that added punch you are looking for.

That AMP is a beast. Agree with Jakewash that the room environment could be part of the issue. You could try a local A/V outfit for an assesment.

If you still want more power, I would get an Emotiva XPA-2 or XPA-3 (based on your 1000$ budget).

I wouldn't bother with an amp at this point. I have to agree it is most likely the mains and not the power.

My recently new M80 loudspeaker has give me the extra punch i wanted

It'll be even better when you get the second one!

Just because your speakers have "built-in subs" doesn't mean they are optimally positioned. Part of the magic of separating the subs from the mains is that it's pretty rare to find that one location is ideal for both. Likewise, not all subs are created equal, and it is certainly possible that the built-in subs don't go quite as low as you might like.

And, yeah, calibration is a good thing. Have you got a setup disk (like Avia or something)? An SPL meter? How do you have the subwoofer outputs from the receiver connected to the speakers? How high is the gain on the subs?