Change capacitors in JVC amplifier

I got an old JVC (HX GD-8) stereo amplifier. this amp is a bit special, because it has two seperate subwoofer outputs on each channel. I'm only using one channel, and I'm using a SEAS L26ROY 10" subwoofer. the problem is that when I play songs with hard bass puches at high volume, it sounds like the amp don't get enough juice to provide all the power.

I found a service manual at the internet, and i disassembled my amp. I found out that each subwoofer channel only had 4700uF caps! is that the reason why the sound (hard punches, not pure bass) sounds weird?

I found some caps on ebay. Do you think 10000uF at each channel is enough? The caps inside the amp is rated 71v. Is it a problem if I replace them with 63v or 100v caps instead? The subwoofer channels is powered by an STK412-430, but I can't find a good datasheet on that one.
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