question

Just in case anyone is interested in doing a similar setup, i've made some progress. This setup touches on non-standard setups with DC-coupling; AC-coupling AND dual-phase use (from 3phase grid).

I was (eventually) able to connect both Quattro (I believe Multi will work the same) with the new RS Multi (the PV/inveter/charger package). Quatto connects via VEBus and RS connects via VECan. I believe the order in which they are connected is very important, as that first connected device is "master". Given RS is not (al least not yet) very "integratable" the Quattro should be first to connect and recognized via CCGX (or other venus OS device). Also, when connecting the RS first, the Quatto went to passthrough, as for some reason the SOC was changed to 80%...

On the DC site, I got a good offer on the lynx distributor and i have ~30kwh of batteries connected. Now, I don't have the full lynx system, but I only needed 4 connections (2 bus-bars from batteries and the 2 inverters). So they are no DC coupled and working well on electrical level.

The next challenge was for them to "talk", for which i enabled the "Has DC" option and it worked, only due to cable length (probably) it showed a different voltage (minor, just .1v difference), I could have lived with that but the SOC is calculated separately, so during the early hours of the morning, when SOC was low, Quattro (who used the BMV shunt) started charging, while the RS continued to use batts. Now, with system setup as per above point, seems the shunt is being shared between the 2 and reports same data).

On the AC side - my utility comes in 3ph system, however, most of the loads in the house (and also the inverters) are all 1ph. Problem is, during winter some of phases drop below 180v and victron disconnects; and during summer voltage goes over 250 and at least the Fronius (but more frequently the Huawei) disconnects, which is a big pain (at least Fronius knows to dial down...).
With the above DC system, I am able to use 2 of the phases AT THE SAME TIME. Since some of the loads will be trough RS and most of the house is on Quattro. This should work pretty good, to ballance the AC. Quattro has 2 AC in, but i don't think it works with grid as it's 120degree shifted.

One final problem i've had, is to use Fronius on AC In (currently on AC-out) as last autumn when I added the RS, it would not charge the excess power (just fed it to grid). I think the issue was with firmware (now running the latest release) but I hope to have time to test in the near future (now it's sunny so topping off the banks).