If the regular RCA connection is not satisfactory I will make some thing that will connect to the higher output RCA pins on the back of the empeg when it is slid into the dock.

I briefly considered bypassing the sled connector, but I had a couple of concerns. One was that the the RCAs have relatively high insertion/removal force, and I wondered if they were rated for as many insertions as the docking connector. The same concern about rating for the DB-9/serial was true, along with the concern that it would be exceedingly difficult to build my own female DB-9 dock that would not (eventually) damage the male DB-9 in the Empeg. This is complicated by the fact that the projection of the power/ethernet connectors into the sled opening would be to a different depth than the RCA/DB-9, making alignment along the axis of insertion even more critical.

Fabbing a whole new sled seems like a lot of work, too. In your shoes, if it was my sense that most potential customers already had a sled they could devote to this installation, I'd consider basing the design on that.

FWIW, I have no problems using the external, lower-voltage RCA outputs with my home stereo. I am lucky now in that all 3 of my installs use some sort of AUX input (no empeg-->amp setup) so I just set Hijack to limit Volume to 0 and leave my Volume set at maximum at all times.