Another mod you can do to both the 219 and 319 is (and do this VERY carefully) remove the high-end booster disk from the capsule. Its meant to produce some reflections that cause the higher frequencies to rebound back to the capsule. It also causes a slight time-smear.
If you look at the capsule, its the disk the same diameter as the capsule, covering the diaphragm with 4 big holes and 4 small holes. Use a jewelers screwdriver and GO SLOWLY!! (if you mess up, you can puncture the membrane) Do one side, put the screws back, then do the other. You could probably get away with doing just the front.
DO AT YOUR OWN RISK!!
Also you can replace the 680pf capacitor at the capsule/board solder points with a 1000pf polystyrene.