You already have an external soundcard with the Lexicon Omega - a Laptop would be ideal to use with it. That way you can do remote location recording, and also do stuff at home, and have the familiarity of the PC recording environment. You should be able to find a new or used laptop with better performance than your desktop PC for the budget you are looking at.

I do this with my PreSonus Firebox - use it at home most of the time, but I've used it also with my laptop for field and remote recording - I even used it with Freq-a-scope for a spectrum analyzer for a live sound setup at our local Jr. High to help tune the system.

Quite handy.

-Scott

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