For what it's worth, I was using the line 6 fbv mkii flawlessly with my midi supported apps until the ios 7 update and now it is an unsupported device and won't work. What a bummer that day was...
Agree with the above posters. If you are short on cash I would unload the ac4tv on cl for a bass amp. Maybe gk mb200, markbass black line 250, or a tc bh250 should all be even trades assuming you are buying a cab to go with it