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