Originally posted by recklessdiffraction ...what receiver do I put on the Nikon speedlights?
Sadly, you don't. You get Godox speedlights instead. If you need to use legacy TTL speedlights cross-brand, then the Cactus V6 II/X-TTL system is probably your best bet, but Cactus is getting out of the business.
Quote: There is the GODOX X2T (Nikon) but that looks like some other type of trigger and it looks pretty bulky to sit on a flash.
It's a dedicated transmitter, not a receiver/transceiver unit. It won't work to trigger a flash on its hotshoe. That hotshoe is if you want an on-camera speedlight as well as an on-camera transmitter. But all the current 2.4 GHz Godox speedlights have built in transceivers and can do double duty as both light and transmitter, so you don't have to do the sandwich thing.
Quote: Will it play with the X Pro P Pentax transmitter on the camera without losing HSS, TTL, Manual control etc?
If we're now talking about the X1R-N receiver, no it will not. It becomes a manual-only trigger. No TTL, no HSS. But you may still have M power control. Unlike the transceivers in the speedlights, the dedicated X1R receivers (which only come in Canon, Nikon, and Sony flavors) cannot do cross-brand TTL.
The two main units you may want to consider getting (assuming you don't need an on-camera speedlight) are either
the TT600 or the
TT685-C. If you need it to do TTL/HSS on-camera as well, your only two choices are the TT350-P and the V1-P. Unfortunately, Godox never released a V350-P, TT685-P, or V860 II-P.
The TT600 is a single-pin manual-only speedlight, similar to a YN-560IV. So, on a hotshoe, all a camera can tell it to do is fire. But the built-in Godox transceiver allows for M power control, group on/off control, and HSS. It is not firmware upgradeable. But. It is only US$60, so putting together a three or four-light setup with one is relatively inexpensive.
The TT685-C (for Canon; $110) is the only TT685 unit that can be firmware-upgraded to be a P-TTL/HSS radio off-camera unit in the Godox system. Unfortunately, the TT685-N cannot. And if you still have Nikon gear, that would have been the better choice (as it can do Godox radio and Nikon's optical CLS/AWL). The V860II-N can be updated for P-TTL compatibility as an off-camera radio unit. But it's more expensive ($180) than the TT685, because it uses a li-on battery pack, which gives is 2.8x the battery life of a set of 4xAAs.
Quote: The only things i have gathered is that the Nikon system is pretty straight forward by comparison.
This is probably because, as best I can figure out, the Godox system was more or less reverse-engineered off a Canon 600EX-RT.
It's going to feel ultra-weird to a Nikon shooter.
Just me, but the best sources for information on Godox I've found are
the flashhavoc website, and
Robert Hall's youtube channel.