A bit of help understanding an IC
If you're only going to use one output, you should use Vo1 since that's what the chip is designed for. But I'm not sure why you'd want to do that. The chip is designed to drive a speaker with differential ("bridged") outputs. Among other things, this lets you connect the speaker directly to the IC with no decoupling capacitor. It also looks like the amplifier can provide more output power in bridged mode.

Also, if you want to do signal conditioning, a power amplifier IC is probably not the best choice. I would suggest either a proper automatic gain control circuit, or (if you need digital control) something like a PGA2310.