I have an SRH550 Home Tuner; can anyone out there tell me what the "service port" is intended to be used for? Interestingly enough, the user manual doesn't even mention it. I assume it is there so you can hook up an external component (e.g. receiver, etc.) for external control, but want to be sure before I actually connect it to my Onkyo TRS706 (which has the same, 8-pin female mini-DIN connector earmarked "Sirius"). Any help would be much appreciated! Thanks.