Best new musical flooring for flooded basement

I don't think what you put down is as important as what you do afterwards. Decouple the mains and sub system.  That will make a big difference..

I lost a record collection 37 years ago behind a refrigerator water supply line.  There are still 300 400 LPs down there waiting for a clean up.. I was sick for 5 years..

It got my whole Beatles collection 45 and 33s and all of my Chet Atkins. 
Merle made it, thank god..

Regards 

If there's a chance of future flooding, I'd put down LVP, which stands for Luxury Vinyl Planking. Looks similar to the various Pergo products, but is solid vinyl, so water proof. After that, soundwise, do what you need to do to tune the room.

Bamboo is said to be very natural and sustainable. 

Had the same situation about 20 years ago. I went with slate & throw rugs. Sounds great & don't have to worry about wet carpet again.

Interesting recommendations. I would have chose a thick pad and high grade carpeting.