Omnisphere Multi issues in X2

I'm using Omnisphere - if anyone is familiar with this instrument, maybe they can help ...
 
When I use one instance of Omnisphere inside X2, and load up new sounds on each channel, I start getting clicks and pops after about the 5th channel.   
If I use seperate instances of Omnisphere, same sounds but on different instances, I get no clicks /pops, even with 8 seperate Omnispheres running.
Something is causing the clicks/pops when in Multi mode - has anyone any idea, and is there something I can do to correct it?
 
Thanks

PC spec:   relatively powerful
HP Z420, Intel Xenon E51620@ 3600MHz, 8GB RAM,  
Windows 7 Pro 64-bit
Soundcard in current use is Focusrite Saffire Pro 24 with latest software/drivers

Each of the 8 instruments in the multi goes to the same midi channel  (up to 8 sounds stacked on top of each other, though the overall levels though are OK, not even in the red ... )
 

The other thing that I'd look at is if you're using an internal fx chain in omnisphere that the sequence might be causing some clipping and if the last fx in the chain is outputting below 0db then the master meters wouldn't show up in the red but it's still clipping somewhere in the chain. Lots of times this will happen with multiple delays.

Hrm. Kinda stumped. Try turning off all the master fx and see if the clicking is still there. I've paid for synth patches that were poorly programmed (i.e. clipped) before. I'll sleep on it too and maybe I'll get some ideas.

Hei Paulo - lots of questions is good.  Its starting to drive me mad (the problem that is, not your questions :-))
 
It happens even if its a new project and with just Omnisphere, nothing else anywhere.   I play my midi controllor and then in the Performance icon in X2 the yellow lines start going crazy, and the line on the left hits red and all kinds of crackling and popping follow.    
 
I tired changing the buffer size, and it makes no difference.  256, 512, 1024, same result.   

"Clips and pops" sounds more like a buffer underrun than clipping. Maybe a matter of CPU load balancing? Trying to think why there'd be a difference between multiple instances versus one multi-timbral instance (which should be more efficient) and all I could come up with is that multiple instances are each going to run in their own thread. Maybe the single instance is maxxing out one core.
 
Some of Omnisphere's patches gobble up lots of RAM. Go to the System page, where there is a memory-usage meter that shows how much RAM Omnisphere is using versus how much is still available. 
 
Since you have lots of physical memory, try running it in non-streamed mode. This will cause Omnisphere to load each sample set in its entirety prior to playback, avoiding disk I/O overhead during playback. Or leave it in streaming mode but increase the pre-load memory allocation so that more of the file gets loaded before streaming starts. Also set the memory limit to "no limit".

The E5-1620 has 4 cores according to the this page

Update:  
Bitflipper, thanks for the tips but unfourtunately did not seem to have any affect.
 
What I discovered is that it only seems to happen on multis of a certain type: in fact those that I purchased from a certain vendor.   The multis that shipped with Omnisphere and other multis I made myself are not affected.  I contacted the vendor about this and they said that is was not unusual when playing 8 large Omnisphere patches simultaneously.   They said they should work on "powerful computers".   I really thought that I HAD got a powerful computer.   Does my computer specs not look enough?   I can easily add another 8GB RAM if it would make a difference.  I thought my PC was pretty powerful already though.    

When I split the multis over 2-3 seperate instances of Omnisphere, then the clicking/popping does go away --- this loses the playability of the original multi which is a pity, particularly when I have a relatively powerful computer to start with.  For those with lower specs than mine, then its also going to be a problem --- I think the vendor should be aware of that ....
 
I havn't yet tried all the Spectrasonics tricks or edited any of the patches to make them less CPU intensive, so I'lll have a go at that too.
 
Thanks all for your help and suggestions.
 

ston
I don't think adding more RAM will solve the problem.  It's a CPU core maxing out its processing capability.  Yours is more or less equivalent to an i7 running at a similar speed, so it's pretty damn good.  Try splitting the patches you want to play across two instances of Omnisphere, does that solve the problem? 

Just an update on this issue, if it could help someone else ---- I now upgraded my RAM from 8GB to 16GB and the problem has gone!   The other performance tips in this thread still help lower the spikes, but now the RAM has been increased I can actually play all those multis which were unplayable before, they now play perfectly.