I got one this week. I couldn't stop playing bass- upright and electric- for 5 days.
Not only does the loop return work as an input, but the send works as a line out.
I've been using this in a large band, it powers a cab/monitor meanwhile sends the PA/in-ears a very very nice tone independent of the master volume (and without the vintage switch).
I've also sent this in various ways -loop send and line out- to the aux in on my big 800W head (not quilter), and damm. With a properly powered bass cab, or a pair of them, this tone is among my all time favorites. I mean it's great at 33w and all, but with the extra muscle it's spectacular to my ears.
And I can just use this with any cabinet for most of the work I do. I'm in pit or church theater pops most of the time, blending with acoustic instruments. I love this thing.