Dont know if this helps any, perhaps just some thinking material. Ive been thinking-looking at small subs too the last month or so. On the Mackie boards there still having some troubles with the 15" powered sub, the box shutting down and such, probably should stay away from that one for now.
According to Mike Pyle, the Art powered 15" is very nice, another small sub to consider is the LS700p, the Art is lighter, takes XLR and is a bit newer in design. For me, the advantage probably would be the Art. Give Mike a PM about these subs, (or the LS700p) he did a small sub shoot-out for me and that is how I received this information. Havent heard anything about the DB sub.
Passive cheap subs? JBL MRX518, TRX118, LS608 and TXD118 just to bring up a few. The cheapest is the TRX and TXD, the TXD will run on a smaller amp and you can even run four of them on a single PLX3402. Out of the boxes mentioned, the 608 has the highest efficiency ratings at 103db vs 95db for the more expensive SRX718. Next the TRX, TXD then the MRX with a 94db,
1w@1m, but the 608 and TRX will need much bigger amps. The TXD is the lightest and one of the lightest subs out there I think at 61.5 pounds while the 608 is close to 100 pounds. Just about all of these subs can be had for the price range your looking at with the cheapest package going to the TXD118 Turbosound subs, 4-boxes about 2 Grand, 1 PLX3402 about $1000.
I would love to hear the difference in sound and output between the powered subs and the small passive boxes.
Almost forgot the QSC powered subs, HPR115 (I think) is a powered 15" sub, weighs around 100 pounds, 700w with a claimed max spl @ 133db. If this is true, this sub should rock! Its around $1000 each. The TRX should be a sweet package, cheap not to heavy, looks real good but Carvin doesnt get alot of love around here where the LS608 gets great reviews from the users on the boards.