TL;DR: MobaPad for Joycon1 rumble motors, GameSir for DualSense rumble motors, GuliKit for acceptable fancy rumble but overall better features. Possible but not worth transplanting newer rumble actuators into existing HD rumble 1 controllers. Watch this space for more controller hacking news.
Special Interest Activated!:
I don't think any controllers use the same rumble modules as the Switch
2's controllers, and I can't find the specs anywhere.
MobaPad
M6 HD have the same ALPS modules as the Joycon1 (I think their pro controllers do too, also the Coiorvis Phantoms, but they don't look as comfortable), so those might be your best option if you want subtlety.
You could get something that has DualSense motors (GameSir
Tarantula Pro or
Nova) or similar (GuliKit
KK3 Max / Pro - 'Maglev' motors). However, these don't feel as nice as the Switch 1 joycons' HD Rumble - the Mario Wonder music blocks make different notes, but there is also an unpleasant buzzing that takes some time to stop (with original joycon, I can still feel that the rumble doesn't stop instantly, but it's less noticeable). The Tarantula has the nicest Pro controller rumble (and also lets you invert the gyro aiming separately from the right stick, in case like me you learned to aim in Ocarina of Time and want to force gyro support in games that don't have it), but has the left stick below the d-pad rather than above, and only two back buttons in useful places, so I prefer the KK3 Max. If the noise bothers you, you can reduce the intensity or use HD rather than Maglev mode, which both reduce the screeching but retain some HD-ness.
It's definitely a software issue, as I have retrofitted an actual DualSense motor into my KK3 Max and it hasn't changed much.
Edit: I ordered a Joycon2 with a sticky ZR button to tear down and try to fit the actuator into one of my M6 HDs. The DC resistance is about 2.9 ohms vs. the original Alps module’s 8.6. With the appropriate plug soldered on (in addition to the original, so I can rebuild the JC2 later), it works and is a bit stronger. But as with the GuliKit controller, it buzzes more. Hopefully I will be able similarly to reduce the intensity a little to get rid of the harsh noises.