AU Lab will not save document when output set to aggregate

I searched but couldn't find an answer to this problem. Whenever I create a document in AU Lab that outputs to my aggregate device (2x USB Muse DAC's used for 2.1 output) it refuses to save the document -- it acts as if it has been saved but no file is actually written to the HD. Everything else works perfectly and sounds great. If the document has anything else as its output it saves just fine. I'm getting tired of having to manually configure my crossovers, delays and EQ everytime I restart my computer. Any thoughts? BTW, "Use Preferred Audio Device" is unticked in preferences so that's not the cause. I'm stumped. :/