Why buy a crate motor with a supercharger on it (for $14K uninstalled) when you can just install a supercharger on your existing 6.2L V8 for around $7K?
Sounds like you'd bought the wrong car if you want to convert from L99 to LS3 (and the A6 costs a little more than the M6 to boot).i got a quote from a well known shop for about $14k (parts and labor) for a magnacharger, cam swap, L99 to LS3 conversion, pulley, boost-a-pump, and all other necessary components with a tune. that would get me around 600+ rwhp versus 550 flywheel hp with the LSA engine.