Ted,
My Vegas has the S&S map in it and, based on the last dyno run, is spot on. Do you still have the stage-1 map or did you get the S&S map when you installed the S&S air-cleaner? If you are still running the stage-1 map, then you might be on the lean side for your set-up. The popping on decel doen't mean much as mine (and just about every other Vic I have seen with aftermarket exhaust) pops.
It sounds like you are describing a dry-type nitrous system. I have only seen these used on large-displacement, liquid cooled auto engines with aftermarket fuel injection computers that could handle the necessary added fuel to go with the nitrous.
If you are planning to run a nitrous system, I would only consider a wet-type where you can include additional fuel with the nitrous. Bikes, as a rule, need a little excess fuel with nitrous for the cooling effect.
For reliability, I would recommend a set of forged pistons. The cast stockers will not hold up well to the extra heat and pressure of nitrous. Also, plan on spending some time on the dyno getting the system dialed in properly if you want it to be reliable.
Kevinx, can you think of anything to add/correct?
VegasRider