Sigtronics Intercome (SPA-400)

Anyone have any experience with Sigtronics SPA-400 intercoms ?

I'm looking to add a stereo music input to it. I found out that Sigtronics makes an add-on unit (RES-401) module and it states that it simply plugs "inline" with the existing SPA-400.

The RES-401 can be had at Aircraft Spruce for $130, but before I purchase one, I'm interested in knowing more about it, so if anyone has some experience with it, I'd love to hear the good/bad/ugly details.

I've got a SPA 400 intercom in my Archer and added the stereo adapter to it. Works just fine. I've had a number of SPA 400's over the years and never have had any trouble with them. By the way, do you know anyone that would like a nice 1977 Archer II. Would like to build an RV-7 to go with my RV-8....

Thanks for the reply, I'll keep my ears open for anyone at my field looking for an archer.