A slight correction:
DA-131 = SPDIF only, Toslink/Coax input selectable.
DA-151 = USB only, slightly lower end than 131
DA-131 is going to be superior to DA-151 if it is fed from a good digital source, such as the M-Audio card you mentioned, EMU121M, RME, or stereo component that provides SPDIF signal.
DA-131's strength over DA-151 is mainly at frequency extension, it extends out further on both ends, and it is going to be more detailed and neutral than DA-151.
DA-131 however was released before DA-151 and comes standard with BB's OPA604. OPA604 while good in its own regard, it is not as good as the LME49710 taht comes with DA-151, and thus we currently offers upgrade to anyone who orders DA-131.
Just add $10 to shipping and handling, and put it in the paypal payment note and we will either include it in the package or install it for you. (Depend on how you like it, if no preference is mentioned in the note, we will just include in the package.)
That's about it I suppose.
