Basically, keep the RayDAT as master, connect the ADA8000 ADAT in and out optically to a RayDAT ADAT pair and set it to external (slave) sync to ADAT and it will just work. I’ve done this with multiple devices and mixed with MOTU devices (828MkII’s). If a preamp has an S/PDIF or AES-EBU input it should also be possible to sync it to the RayDAT … for example, if you retained the EMU 1616M on a separate computer you could send either ADAT or S/PDIF to it and set it to slave to the RayDAT. Don’t forget also that you can use the RayDAT’s S/PDIF and AES as two separate and independent stereo channels (2 stereo ins and 2 stereo outs), so you could have a 2-channel preamp coming in on S/PDIF, a stereo monitor amp on the S/PDIF output, another 2-channel preamp coming in on AES (XLR) and finally a stereo headphone channel going out on AES. After that, you still have 32 in and 32 outs available via ADAT
The main problems are when you want to connect a preamp that only has an S/PDIF output … this is common with many guitar effects and pedals. There’s no way to get these to sync to another device; the only option there is to sync the RayDAT to the device, in which case you lose out on the quality of the clock from the RayDAT. One notable exception in the guitar world for example is the Behringer V-Amp Pro (the 19" rack version) which has a word clock input – which brings me neatly to word clock.
If the budget allows, I’d strongly recommend getting the WCM along with the RayDAT as this adds word clock in and out, however it could always be added later. I’m still kicking myself for not getting the EMU word clock module when I bought my EMU 1212M years ago, while they were still on the market!
In a nutshell, as far as sync in concerned, with the RayDAT as master, what you need to be able to do is send an output to the input of each device that you want to operate in sync – and each of those devices must allow itself to be set to external sync as well! A device which has no digital inputs at all cannot be slave-synced to anything.
I’ve had a look at your thread over on Gearslutz and it’s all pretty good advice as far as I can see, although I wouldn’t worry too much about the recommendation to use the clock in the converters as opposed to the RayDAT (unless of course, you have very, very good converters!). Why that advice is given (and this applies to A/D conversion only, i.e. recording) is explained by Hugh Robjohns in an SOS article. Note however that if you use word clock to the converter (ADA8000 in your case), this “interface jitter” won’t happen; another argument for word clock. Hugh writes a more in-depth article on the subject here and if you want some real food for thought then have a look at his article on whether or not anyone benefits from a dedicated digital master clock at all!
Finally, don’t forget that RME’s TotalMix is simply awesome (not a word I use lightly, as is the fashion!). Think PatchMIX on steroids.