But a lot of DI outputs on bass amps (most?) are line level, either solely or as one of two options (the other being mic). The fact that it's a line-level out doesn't make it not a DI.The XLR output is labeled “Line Out”. Sounds more like something to use with an external power amp than a DI to me.
Also, I can't imagine that needing to hook up an 800W amp to *another* power amp would be more common than just needing to get a direct signal from your amp to the PA. Who knows what the actual numbers would be, but it wouldn't surprise me if for every 1 case of the former, there are 100+ cases of the latter. This suggests that the Quilter's line out is conceived as a DI primarily, and that its ability to drive another power amp is probably a secondary consideration (gravy, IOW). To paraphrase Charles Barkley, I might be wrong, but I don't think so.
Besides, if that line out isn't meant as a DI, then the 803 doesn't appear even to have a DI, which would be significantly weirder than not having a pre/post EQ switch. But then, Quilter is indeed quirky sometimes....