I spent ages trying to find something similar to use with my mini bass as the ultimate travel rig. On top of your requirements I also wanted reverb, compression and battery power.
Theres nothing. Might have to invent something.
Edited to add actually the closest I got was a bass cube which has the benefit of speakers, ok less portable but still. Only thing - no DI (not a problem for me) and the compressor is a bit savage.