I got to sample this cool device at my local Music Store and I was way impressed by it.
The device is a Vox PreAmp which is battery powered and plugs directly into the guitar and the speaker is a pair of headphones. According to Troy (again at my local music store), a good pair of headphones makes a big difference over a bad pair of headphones.
Anyway, the sound is super impressive. The are 3 models and the one I listened to was AC30 which had a really nice clean sound.
I’ve tried one device and seen other devices that might be good quiet listening devices (you know, play while others are in the room kind of thing) but they were not very good. This one really feels like it could be the one.