No, grounding cables aren't standard in car audio installations (but as we supply them this shouldn't be an issue) - but then again, feeding the output from the empeg into another head unit isn't too unusual either (Kram has a Philips navigation system in one car and an Alpine multimedia system in the other with no problems once the grounding was correctly done, and Steve, the business director here has his empeg feeding into a Sony CD head).

It still sounds like a grounding problem, but by all means try the line driver. You may need to ground the outputs of the empeg to the line driver case - basically, your mileage may vary.

Hugo