I just bought that little Vox Bass Headphone amp. Soooo easy to plug in my MP3 player and learn songs. And I can practice late and not wake the house.
Sound quality is very good too. I was playing one of my basses through it and thinking why doesn't this bass sound this good with my amp... You've got to use robust quality headphones, but it handles a low B no problem (actually Bb in my case).
No problem with my Series I. I've used it with other passive and active basses and it works really well.
I haven't blasted the volume, but at practice levels, nice full sound.