there is adapters out there that convert steering wheel remotes to IR for various head units talk to a decent car hifi place and they should be able to point you in the right direction. Then using Hijack you can get that to drive the empeg.

Also there is something somewhere that someone got a Mk1 to work with a sony remote and a puegout stalk so it is possible

As to running it through the standard head unit i think that would be most difficult i would say sod it and buy an amp and an adapter plate and run with empeg only.

There is another option for the remote it gives you an excuse to buy a Mk2 and a radio module and use an adpter to a sony stalk from vectra buttons