Hi. You certainly could try plugging it directly into the wall and see if that makes any difference. Might not help, but it sure won't hurt. Well, as long as you're not in the middle of a lightning storm, that is.
BTW, do you have the speaker impedance switch set to 6 Ohms? If so, I suggest switching it to 8 Ohms. The lower setting just limits the current flow, but the amps shouldn't be at risk with lower impedance speakers because the receiver has a protection circuit. If the "AMP OVERHEAT" trips, then set the impedance switch back down.
What makes you question the power? Does your audio sound "muffled" or lack dynamics at high volume? If so, I experienced a similar experience with my VSX-1015 years ago. When I got an amp for the front two channels, it really helped with the overall dynamics because it provided more power for the front two channels and lightened the load on the receiver, allowing it to power the other three speakers without any issues (at least, in my set up).