Splitter.Or.... some amps have output jacks so you can plug another amp in as it sends the signal back out. My Legacy amp has this feature. I used to have another amp hooked to it driving the rear deck speakers. Also, If its a bridgeable amp, you can run it with the sub bridged and your L&R speakers hooked normally. I tried this for awhile too.
If it can be hooked up a certain way, i have to try it out.
04' Olds Alero
91' Colt GL hatchback
4g15 12valve 5spd.
4g37 TB, MAF & Injectors. 4g37 ECU
Ported & polished & custom CAI w/K&N filter
5* Cam retard, 7*Ignition advance
2-1/4" catback w/flowmaster muffler
89 GT brake and suspension swap
Lots of little s#@t