ASRock 939Dual-VSTA + DS2416 - two strange symptoms

Long Story Short
Problems with new DAW.

-snap crack pop durring heavy cpu load playback unless USB midi 5x5 is conntected!
(strange I know, must be a mobo thing?)

-playable latency (via midi controller) gets worse and worse as CPU load increases.
Soft Synths are not playable if CPU is near 50% Load or higher.
Totaly fine when CPU load is light.


Long Story
So after all the raving reviews of AMD X2, I've decided to take the plunge.
Just bought myself an ASRock 939Dual-VSTA and a X2 3800... :)

I had to go with that mobo because my legacy sound card (the Yamaha DS2416)
is known to work with very few select boards.

The ASRock 939Dual-SATA being one of them. (that users here had no complaints with)
The ASRock 939Dual-VSTA is the same with the exception of SATAII controller added in.

Being an "Intel" guys for 15 years or so,
I have a few observations, and questions I would like to share with you.

I put everything together and it seemed fine.
I had few RAM problems initialy, that I've ironed out.
Mobo did not like 2 paris of slightly different RAM, (Samsung Rev.D and Rev.E)
so I'm running on 1 pair now and everything seems ok.

Few odd things I've noticed after the build.

I installed the AMD Dual Core driver and the patch, then Sonar.
In Sonar I created a test project that consisted of a stereo audio track, and 5 reverb fx.
Set my latancey slider to 5.8ms and continued to multiply the test track untill I started noticing problems.

I got to 20 setereo tracks with 5 reverbs on each, totaling 100 reverbs! (not bad for horsepower)
only problem being ... snap crackle pop.. w/ cpu around 75-80% !!! hmm I thought.
Tried two different PCI slots, no differance, tried this and that, no help, then stuble accross something wierd..

As soon as I hooked up my MOTU midi 5x5 (via USB) the snap crackle pops went away!
Only the odd one at loop point.

It's strange but the presence of my midi device repeatedly affects my audio quality.
Must be related to USB/PCI bus traffic and latencey timings, but adjusting my PCI latencey in the BIOS
has not seem to of helped. (it does affect the CPU usage though)

Another stange thing I've noticed....
My playable latencey (via midi controller) is fine when the project's CPU load is low.
5.6ms or anything under 20ms in Sonar feels like it should.
As soon as the projects load starts getting to 50% CPU useage or higher,
my playable latencey is .. well... unplayable :) don't think I've notived that on any Intel chipset rigs I've build.

Has anyone with a "uli" board or any other for that matter noticed this? Any cure? Am I SOL?

I know there are other users on this forum w/ DS2416 and the "Uli" board.
Would love to hear your feedback about playable latency with projects over 50% CPU load.
This midi 5x5 affecting audio quality is whack too.. I'm starting to wonder if this baord simply sucks for audio..

Thanks,
Tomek.

-edited subject for clarity