I think you can use the pre-amp outs from the Outlaw to feed another amp. The internal amp is not cut off when they're used.

For volume matching I'm not so sure. I think any trim control done on the Outlaw is on the pre-amp signal, so it would apply to both amps. I think you may need to match the Outlaw's power rating with the other amp, unless it has a volume matching pot built in.