Strange High CPU behaviour

[Rosco1969]

Hi All,

Came across this little puzzle today.

iMac i7 3.4GHz, 20GB ram, OSX 10.8.5, Protools 11.3, Focusrite Liquid Saffire 56, ART TubeOpto8 (via ADAT)

I have a tracking session set up with the following:

1x Track assigned to click
10x tracks assigned to record drums
2x tracks assigned to record bass
2x scratch guitar tracks with Scuffham S-Gear instantiated
1x track assigned to record a scratch vocal

I have 5x aux busses each assigned to different pairs of outputs for 5 different headphone mixes.

Each audio track has a send assigned to them going to the 5 headphone busses for monitoring.

Buffer set to 64 samples, WIFI off, Bluetooth off.

Here's the puzzle.

As soon as I record enable all the tracks the CPU pegs out at 100%, bounces around a bit but stays way up around there.
If I take the two guitar tracks out of record, the CPU sits around 25/30% and stays there.
If I re-enable the guitar tracks and set the buffer to 128 samples the CPU sits around 20/25% and stays there.

Now, if I set the buffer back to 64 samples and record enable all the tracks, again, the CPU jumps up to 100% and pegs out.

Then, if I "make inactive" or delete the 5 headphone busses the CPU drops to around 30% and stays there fine. If I "make active" again then the CPU pegs out again at 100%

At first i thought it was S-Gear causing the problem but it's the same with Guitar Rig 5 and Amplitube 3.

I've managed to narrow it down to the Busses for the headphones.

Why would the headphone busses affect it like this? Is there any reason or explanation, suggestions?

As I say, buffer at 64 samples, 2x S-Gear, all tracks record enabled and WITHOUT the headphone busses, I can record all day long with the CPU at around 30%. WITH the headphone busses it won't even start to record… pegs out at 100%

Sorry for the long winded post but I'm a little frustrated with it at this point.

I'd like to be able to record at 64 samples and monitor this way but with this problem, it's impossible.

HELP!, lol

Rosco