I've been using the Shuttle 6 for the last couple of years and have been extremely pleased. It has proved very reliable and plenty loud enough for my needs.
No issues so far, other than a crackly master volume knob, which I think a few of them have suffered from. All sorted with some switch cleaner.
On one gig it got a bit sulky and cut out momentarily, but we were being powered by a generator, which I think was the problem.
I've been using it with Mark Bass cabs so not sure how helpful my opinion can be given you cab choice is very different.
Are you after getting the same sound as your current amp or something different?
All the best, Gary