Hi
RME driver are in last version
PT 12.8.2
Message error if trying to sec at buffer 32 with plug in activated : A CPU overload error occurred. If this happens often try increasing the HW Buffer size i... or removing some plug ins ( AAE-6101 )
Today I tried to deactivate the Hyperthreading ( with Xcode app ).
It s much better. Less cpu usage and more stable . 
For a session in 48k 24 bit,
buffer 128, 9 tracks in rec mode, 46 tracks in play mode, no plug, no send I obtain :
Hyperthreading activate ( 24 core ) :
cpu 17-34% 
Hyperthreading deactivated ( 12 core ) :
cpu 10-15% 
For the same session at
buffer 64 I obtain :
Hyperthreading activate ( 24 core ) :
cpu 47-67% 
Hyperthreading deactivated ( 12 core ) :
cpu 19-25% 
I didn't tried with the Firewire Apollon Quad Audio converters, but the results are very satisfying.