After some looking at alternatives I indeed followed your advice and got a ET8500 with 4 tuners to act as the server box moving the ET9x00 to a client-role. A worthy upgrade if I see the speed difference compared to the ET9x00
Using the fallback option works very nicely, but unfortunately only for FTA channels. The channels that are encrypted only work on the server that has my cards not on the slave-box, so decryption isn't happening on the server but on the client. Looks like I'm still missing something here to get this to work properly. :-(