I was curious about using this device to extend line level audio. What I found was that it transmits more than enough spectrum for a sub woofer, and it has a smooth roll off in the vicinity of 5 KHz or so. This is important, because you don't want it to interfere with your crossover frequencies.
So, this device isn't really suited to extend music to another line source, which is very disappointing, but it would be suited to extend voice quality audio to another room.
This could be an idea device for extending conference call audio, paging audio, to another powered speaker. If the powered speaker has a treble control, you could definitely squeeze some good speech diction out of it (the T and S sounds).