Last (and easiest) ones first, Rich...
...Are the mic model eq curves still available when going with a Heil capsule?...
Those Line 6 models (that "live" in our handhelds) no longer have any effect when another maker's capsule is screwed on.
...Should I just turn the filter off?
Most of us find the "Norm" filter at our receivers to be really handy with a variety of models, capsules ...and vocalists, …speaking of which...
Aversion Therapy For Vocalists
- Engage the really harsh "Talk" setting at the receiver and blame the resultant "disappearances" on the offending singer's hand and/or incorrect proximity technique.
- I find that a the tactile effect of a foam wind-gag seems less "finger friendly" and so tends to discourage the behaviour in question. (As you'll see below, one will probably be required anyway to cope with the extended bass response, ...should you decide to go with either of Bob Heil's wonderful capsules.)
- An electric cattle prod (from your local rural supplier) can be extremely persuasive, when applied judiciously.
...I'm thinking about getting either a Heil RC22 or RC35. What are the differences between these capsules? Which one would be better for a singer who isn't always "on" the mic (regardless of how many times I've told him to stop doing that...
I happen to love BOTH of those mics, (wired and/or wireless versions) but, (in common with all "close vocal" mics) both will only truly "deliver" when correct techniques are used, …exactly as you've grown tired of pointing out to the singer in question.
My feelings as to the differences ?
To my ears the 35 has a slightly smoother and more "ribbon-like" bass than the 22, which I guess makes it the marginally "better" sounding of the two, with both having very "natural" and "open" mid-ranges and tops.
On the road, (as distinct from the studio) that extended bass seems to make the 35 require more filtering and/or eq of that bass region to control both "rumble" and "whoomp" feedback, should either present themselves.
Regardless of individual vocalists, I would always recommend employing a urethane "popper stopper" windgag with either of these capsules, as both of them can faithfully pass plosive bass "pops", but the alternative of using electronic "cures" for that often also reduces the fabulous smoothness that we've paid for.
Which one ?
For what we do, I marginally favour the (roughly) $40 USD cheaper RC22, …but I'd be very surprised to hear of an XD-V user who's unhappy with either.