That's what I'm in the process of doing for a room in my basement as well (for the same reason, music room). Did you use that flooring that just pieces together like a puzzle, or is that the true hardwood flooring? I was thinking I'd put laminate down, or even hardwood, but the kind that's easy to install (so they say). Anyway, your room looks great!
I've heard that bare floor is good for acoustics, but if you want to do recording, carpet is better. Not sure how true that is.
We put down stuff called "dricore" subfloor system first. Its basically 2'x2' plants of wood with corrugated polyethelene (i think) (plastic) stuff underneath to stop moisture and allow air to ciruclate. Its about 7$ a piece I think so its a bit expensive. However, before all that, we had to level MANY spots on the floor (like 5-6 spots, each ranging from 1ft to 5-6 feet) that were uneven. We did this with "self-leveling" cement which you can get at any home depot. Just ask. The dricore manual says you have to level, with cement, any low spots great than 1/4". Anything less than that, you just buy these shims (like 4$ a box I think or something) to put under and make it nice and level.
Next, we put down the foam stuff. We then installed the actual wood flooring. The stuff we used is laminate flooring. It just locks together. We bought ours at home depot. I forget the brand though right now. It really does take 2 people installing to do a good job (at least on the brand/type we did). One person has to hold the previous tile up and in sorta, while the other person installs the next plank. You also have to tap them in as you go and later on, to ensure the seams are not visible. Fun fun. :tongue:
I am loving the sound of it! Playing my piano down there just sounds so much better. I suppose for recording you might want some acoustic tiles, but I just love this floor too much right now though haha.
Best to talk to some professionals though, so dont take my advice as fact