+1 on a low mid voiced cab for loud upright gigs. I've had the MAS 18 out on a couple gigs that started pretty acoustic but devolved into loud electric by the end. The 18 worked fine but I had to shape the lows quite a bit as there is just so much going on there with upright. For that stuff I would have prefered a cab that cut through better, a more traditional bass guitar oriented voice. I usually prefer a tighter low end with upright as piezos can put out a ton of unnatural sounding low end with a deep voiced cab. The tighter low end voice of the Doubleshot has so far been great for me but I don't have much experience with it on louder gigs.
Since my MAS 1/8 is powered by a 700-1,000 watt Ice Power Module, I've not yet hit a gig where that cabinet wouldn't keep up, however I can see where that would be a problem. With a Grace Felix you can "filter out" the low end garbage that might be an issue.
It's pretty darn loud with my Lakland 55 94 and the low B is tight and full through the 1/8. The only cabinet that interests me in the GR Bass line is the 110 so my reason for getting one is purely low weight, compact footprint and primarily smaller gigs where you
have to walk in fit into a tight space like a cockroach.
