[bedoig]

Ya, Audio Manager is pretty nice. If you run HTC Home, it integrates with the audio tab as well. There are a lot of nice players out there, but I've always liked the simplicity and functionality of Audio Manager.

To trim songs:
Start playing the file, hit Menu, Set as Ringtone, Trim. It won't overwrite the original, so no worries there.

Unfortunately, I don't think there is any way to modify volume levels.