I am actually using an RME 9652 with an external 24 track hard disc recorder. So far I prefer this to any soundcard setup I have used yet. I don't actually record anything to the HD recorder, but I leave all 24 tracks in input monitor mode. I run the 3 ADAT optical ports to the 3 ADAT optical inputs on my RME and actually do all of my recording in Nuendo. Then I run the 24 analog TRS outputs from the HD recorder to 24 tape inputs on my analog console. What this does is a few things. In this configuration, my HD recorder acts as a splitter. I get a latency free copy of each used inout at my console, while sending the ADAT optical signal of the same tracks to my RME card for Nuendo. This also means the HD recorder is my D/A and A/D converter. I like it for a few different reasons. First, NO latency (well technically there would have to be some, but my bet is that its well under a microsecond and undetectable to anything except really high end testing gear), second, I don't have to run any sort of seperate applet (like MOTU's cue mix) so its easier and quicker to route things. Also, I have the freedom to dump a project to the HD recorder and add tracks at a remote location without having to haul around my whole CPU, monitor, etc...
I do however monitor reverbs on aux sends through Nuendo though while I am tracking. Basically, I create a new channel in Nuendo that is setup to recieve an aux send from my console (i.e. aux 5 from the console routes to input 23 on the HD recorder, to a channel labeled rev 1 in Nuendo setup to record from channel 23 on the ADAT optical bank). Then i go into the channel strip for the rev 1 channel in Nuendo, activate the input monitor button, and pull the channel output fader down to inf. Then i go to the channel aux send for the rev 1 channel in Nuendo and load whatever reverb I want into aux 1, make the send prefade, and dial up a good level. That way I have access to any effect in Nuendo that I might put on an aux send in a traditional analog setup (typically just reverb and delay, maybe a chorus or a flange for certain things). There is a latency involved during this situation, but for a time based effect like reverb or delay, i have never had anyone notice. Since my delay is only 6 ms, I can just live with it, or adjust all delay and reverb times by 6 ms. For some singers, i actually let them monitor both the latency delayed track through Nuendo and the dry track on the console because it gives a vocal doubler effect that some singers really like to hear in their headphones while they are laying tracks down.
Sorry about the long post, I didn't start this reply with all this in mind, but I have met a lot of Cubase and Nuendo users who weren't aware that things could be done this way.
