ITS Telecom
I use 2 of these MusicTel-Net + units at my two PRI sites. They are remotely managed via a small piece of software. You can adjust the volume level output as well as running multiple mp3's. They work great and I have had zero problems with them. Very reliable.
Of course, it would be ideal if I only had to run 1 of these, but 2 isn't bad. For us, we have all 13 of our sites accessing the PRI trunks at the two sites, so it works. If each site had it's own trunks, that would be a different story.