I am wondering if you know of any surefire path to nail sibilance, IGD and tracking without spending a massive amount of money.
Now I here that Doug found his arm can pass the IGD trick.
Must be Doug's alignment skill, yes :-)
Nope. FWIW, here's my experience...
My Shelter 901 suffered unacceptable IGD and nothing I did helped. Not multiple alignments. Not even changing from an $800 OL Silver to a $4K TriPlanar.
My first change that profoundly reduced IGD was switching to a ZYX Airy 2. The Airy 3 was better, and two higher models (Atmos and UNIverse) produce no IGD that I can hear on nearly any record (assuming the rest of the system is up to snuff).
ZYX's former US distributor, Sorasound, is selling off their remaining stock at deep discounts. An Airy 3 is now just $1895 (I paid $800 more for mine). The Atmos is just $2495, a huge bargain for a cartridge that comes close to the top class. An Airy 3 or (especially) Atmos would address your IGD and sibilance problems (to the extent any cartridge can). They'd also provide a major performance boost vs. your existing cartridges. An Atmos would be a stupendous upgrade, too much cartridge for your rig at the normal price. I only recommend it because of the sale. (A UNIverse would be overkill in your system and irresponsible of me to recommend, even at a discounted price.)
Lest anyone think I'm pandering to ZYX, I'll add that Dynavector XV-1S, Lyra Titan i and Transfiguration Orpheus also have no IGD problems in my system, and they all rival the Atmos in playback quality. But I don't think they're available at Sorasound's fire sale prices. I'm pandering to value.
Upgrading the drive of your TT should also help with HF distortion and will reduce distortion generally. Short wavelengths (high frequencies) are very vulnerable to distortions in the time domain, which is what TT speed control is about. Consider the SDS or some controller if you don't already have.