Yes, you are pretty well stuffed for recording stereo* with the Solo. The box does not even have a 'combi' XLR input whereby you could have at least got two line sources into it. I can never see the point of these 'one lunged' interfaces for anyone with any pretensions to recording music? OK for podders but then they can find more than adequate electronics for a lot less.
*You COULD I suppose use a DI box on the mic channel? The response would however be less than 'flat' and so you would get two channels but crap 'stereo'.
Dave.