By default, I'd recommend either the EMG 81x/85x(or 60x) set, Duncan Distortion/Jazz or Full Shred set, DiMarzio Dominion set, or Lace Drop N Gain set.
Not much into DiMarzio, I have a RC-600 which has a Tone Zone and Air Norton, not impressed. I was thinking of SD JB/Jazz, also Drop N Gain was on the list. I would like a set of Actives, but this has passives, and I don't really care for the pain of adding everything to put actives in. Budget probably around $200 for a set, I figure that would get me pretty much anything worthwhile.
Honestly, EMGs are hard at all to install, since they use the solderless shit now.
And I'm not a fan of the Tone Zone, either. It's got too much low end and not enough high end for my taste. The Dominion is pretty much the opposite; much more emphasis on the midrange and the high end, so it'll help with low-tuning clarity. The Distortion may be better than the JB for down-tuning, IMO.
And if you don't want to go EMG, but want the active sound, try the Drop N Gains. Probably more faithful than the D-Activators, also IMO.
I have a set of Aylum + up for sale. Neck is wound with the offset for the PRS scale length. Handle drop Bb. With or with out covers. $125 shiped for the set.
I would like to go EMG 81/85 or the 81/60. I forgot about the Distortion, that is a good point on drop tuning it would be better than a JB. I have been looking at the Drop N Gains quite a bit too.
I'll take a look at the EMG site to see what it would take to put those in.
When I got my 85, it cames with everything (wires, a jack, a volume and tone pot) except a pickup selector, which unfortunately costs like $35 for a solderless one. You can get around it buy getting Guitarfetish's solderless pickup selector, or you can use the stock switch and follow EMG's instructions to solder it to the solderless system.