realtime export cpu-problems

Hello there,

since I don´t get any answers in the Nuendo forum, I ask here, since this seems to be a common problem on both platforms:
I am using Nuendo 7.1.2 on a Mac Pro (2x 3,06 GHz and 64 GB Ram), RME Fireface 800 and outboard Lexicon PCM96-Reverb. Everything is synchronized by a wordclock (Rosendahl Nanosyncs) in 44.1 KHz.

I would like to use the Lexicon as external hardware reverb and I am sucessful doing so during playback an mixing.
But when it comes down to exporting (in realtime) a multitrack project (12 tracks) with the Lexicon on the Main output, I run into constant breakups caused by CPU-problems.
I do not use extensive plugin-work, since I am mixing classical musc: EQ here and there, some Multiband-Compression and the outboard reverb by Lexicon.

What I tried:

  • Disabling “Asio Guard”
  • Disabling Apples “Spotlight” (read about that somewhere)
  • increasing the buffer size of my Fireface 800 up to 1024
  • Reducing the bitrate of the export to 16 bit only.

—> Still not one sucessful export so far!

Is there any new information considering the realtime export in Nuendo and the CPU-problems caused by that?

Thank you so much in advance and have a grat day!