OK, I read the manual one is for input the other output. So I guess both are needed unless you have other CV equipment.
With both connected will you be able to patch between the two?
The VX-351 is the Output CV Expander, which works for either the Voyager kybd or RME. This is an optional accessory since not everyone needs or cares to bother with CV’s. Of course, if you are interfacing with external CV gear, the VX-351 is highly desireable.
The VX-352 Input Expander is an accessory that allows you to apply external CV’s to the RME. Optional, again because not everyone needs to interface to external CV gear (the Voyager keyboard has CV input jacks on the back panel, so it doesn’t need a 352).
With both connected, you can patch between the two - but why would you need to? Is there some modulation configuration that you can’t get using the RME alone?
Greg
So for an RME owner to enter the world of modular synths we are talking VX-351 + some other CV equipment with audio output. If you want to loop back to anything other than the audio in on the RME then the VX-352 is essential? Does the CP-251 also connect to the input port? Could you use both the VX-352 and the CP-251 ?
Yes, you can use them both.
So to expand the RME you really need both VXs + other CV gear like the CP-251? In the meantime is there much point in getting VX-351 and CP-251? Long term though the RME + VXs is surely a good core for a modular set up.
The best way I can explain it is if you have outboard CV gear like the MFs, get the VX-351 to control them (except the touchscreen section won’t apply). A CP-251 will add more flexibility and control and can be used instead of or along with the VX-351.
If you want to modulate your RME with external CV gear like the CP-251 or MFs, get the VX-352. Except for using a mult instead of a mixer with different CVs, you can basically route any CV source to any CV destination.
The CP-251 can be used independently of the VX-351 or VX-352 so it depends on what you want to do and with what gear.
I want to have more routing possibilities to create more complex patches by connecting another LFO, inserting some effects / shaping would be good and being able to modulate these. Basically using the voyagers patches as the core of a modular mono setup, aiming for prominent effect lines or complex lead patches. So when will the VX-352 be available? What are some interesting modules to get that open up areas unique to modular synthesis?
The MFs are effects with VC so they are good for the system you are describing. You get way more out of the Voyager using the modules and MFs so I recommend sticking with Moog since you already have the RME. Some of the MFs have LFOs in them so you can start with say the MF-102 and the 352 and work from there. I believe the 352s will be available soon. I’d call Moog and ask them for the exact release date.
It depends on how much you can spend. If money is not an issue, get all 6 MFs, the 352, a 351, and 2 CP-251s and you’ll have A LOT to keep you busy. There are several companies that make modules that can be used as well so it’ll take research to build your dream rig. If money is an issue, get a CP-251 and an Electrix Filter Factory which has CV from Ebay.
Quite right about the Electrix Filter Factory. It’s a multi-mode filter providing LPF, HPF, BPF and Notch filter responses, in either 2-pole stereo or 4-pole mono mode. It has separate CV inputs for the left and right channels, which makes it fit nicely into a modular CV setup.
Cool to patch the Filter Factory in the Voyager’s Mix Out loop, to alter the oscillator sounds before they hit the Voyager filter. 
A lot of music-making potential here. Electrix has discontinued the product, however, which is why you’ll have to search Ebay or troll through your local music stores to find one.
Greg
OK, thanks for all that info, some different ideas there the MFs could be interesting as could some of the Blacet modules. But I think I will be waiting for the VX-352 to get the most out of the RME, I am guessing that aside from insert effects the modular options would be a bit limited without this. Unless I bought alot of other gear and then the voyager would just become a tone source in the setup rather than the centre of it.