You have a couple more options...you could always use a tape adapter to pipe the Empeg output into your head unit (is better quality than an FM Modulator...I've used both).

The other option is to get an aftermarket head unit with an auxillary input and pipe the empeg into it and use its built-in amp for output. Of course that will cost about as much as buying a 4 channel amp. I went that path because I already had a decent Pioneer HU with AUX-in and because I could continue to use my head unit's tuner and CD player (albeit rarely) and avoid buying an amp.