Harmony's database is kept current through users sending the remote control IR signals to the website. If your product is not listed, you'll go through the teaching process, then that model will be loaded onto the public website so that the codes will be available for everyone else. On Panasonic's website your SC HT-400 looks similar in features to the SA-HE100, which is already in the Harmony database within the Receiver devices. You'll be setting the HT-400 up as a Receiver, and the Harmony should have no difficulty operating it.
Since your Harmony will operate by switching the source inputs to the receiver, your functions (Dolby Digital, or whatever) set up within the receiver for each input will remain untouched, and will continue to operate the way they do now. You'll be able to add these functions to Harmony's buttons if you wish to access them directly. If you don't bind them to buttons, they will still be accessible through the menus that the Harmony website will build automatically into your remote.
Same thing with your Apex AD-2500--after you teach the codes (takes about 1/2 hour), it will work fine. I programmed in the codes for one of my devices, and they'll soon be out there for all to enjoy.
Send a message to Harmony at
[email protected] and they will be able to confirm this for you.