[LAU] Sound card or DAC to hook everything together?

Hi all, I'm planning what to buy a small studio. I have two active monitors that have XLR inputs only. I plan on adding a subwoofer when I can afford it, which also has XLR only. I have several keyboards. From just the keyboards my idea is easy: Hook them all to my main one, the Korg Oasys, and take the unbalanced outputs from the Oasys and hook them up to the monitors via TRS to XLRM Cables. Putting linux in to the equation is where I'd like some help please. I also want to use these monitors with linux as computer speakers. I think the m-audio delta 66 is well supported by linux and has a breakout box, so I would also be able run TRS to XLRM Cables from the breakout box to the monitors. At some point i'd like to hook up the keyboards to Ardour too for recording. If all that is possible, how do I switch from using the computer for sound to my keyboards - without swapping cables? Ideally an 8 channel mixer would allow me to switch between a computer and my keyboards, but that seems overkill as my keyboards have everything a mixer would do in my case (eq, effects, multiple channel inputs, midi etc). I am probably missing a simple solution, any ideas? I looked at DAC's as an alternative or addition to the delta 66. These are expensive, but about the same price as a mixer and might be a better fit for the multiple-audio-sources to stereo issue I have. Any experiences with these and linux? Thanks! Robert