AspiSys sells their ASMAX series which I may have to buy if someone else doesn't offer an alternative. I currently use Radio Systems' I.AM.Radio transmitter and ATU. I like both of them and will continue to use the ATU as long as possible. Although I'm still looking at AspiSys' DRMAX series of DRM transmitters, I'm having great difficulty communicating with the company since they don't sell their DRM transmitter openly. Personally, I'd like other alternatives for a Part 15 DRM or AM stereo transmitter anyway.
Maybe the builder of the SSTRAN can add AM stereo capability to his transmitters?