I thought I heard some reverb. Nice touch on EA's part to include this. I set "Hell's Bells" (album version, no editing) as my intro song for the Baby Pens in my BAP career and it was friggin' awesome. It lines up almost perfectly with the game intro, as you hear the bells when you're in the tunnel and the guitar comes in almost at the exact time the players hit the ice.
As for the low volume of custom audio, I tried lowering the other volume settings to compensate late last night. I couldn't get a good read on it since the wife was in bed and I had my surround sound down pretty low. One thing I did notice was that this will only help if you use custom audio for all arena music. The stuff I left at default (stoppages in play, away goal, etc) was blaring.
I plan on addressing this in the first list of stuff I send to the EA community manager (CM for future reference). Maybe they could do something with a separate custom audio volume setting or adjust something behind the scenes to make custom audio volume closer to that of the default playlists.
I'm only speculating here. I have no idea if this is possible or if EA would see it as something that should/could/would be done.