MOTU PCI audio interface - PCI-X vs PCIe experience - HP XW8400

I was running HP xw4100 3.2 GHZ using a PCI-X MOTU interface it worked fine. 
I upgraded to HP xw8400 with 8 cores and the PCI-X interface did not work well.  Interface recognized but it would not monitor itself.  The Motherboard of the HP xw8400 had three PCI-X slots available with several speeds (100-133), all attempts to change slots and reinstall failed.  I could not monitor myself through the MOTU 2408 interface (this is essential). 
The Cakewalk support pages did not reveal the problem.
MOTU told me in a trouble shooter email as registered user (it's a problem with the Host Software (Sonar). 
I took the chance:  I upgraded to PCIe and now it works perfectly.   
My personal analysis:  1- The new motherboard with 8 cores simply outran the old interface and the old PCI-X could not keep up... 2- Or, the HP xw8400 preferred the PCIe. 
Either way some of the newer and faster motherboards may require a PCIe interface. 
PCIe was $295 direct from MOTU.  
 
email me direct if you need additional details:  dbrown12      nc rr com
 
 

I'm absolutely certain.  Said so right on the box, (I still have the box) purchased in the right time frame, looked exactly like the one in the middle at MOTU website, the PCI connectors were right..  Yep I'm certain.  It seemed dumb to me at the time I ordered it but....  now it's working. 
 
It may have had something to with the motherboard or anything else!  No way to tell unfortunately as a home user I don't have the testing equipment to track that down. :-( 
 
The uniqueness of this motherboard with 2x four core (total = 8) and multiple PCI slot types (all types represented) may be part of the problem.  This computer from eBay was probably used in a video production studio with 4 SATA HD's, RAID on one pair of HD's, 2 DVD burners, Win7, video card that takes up 2 slots (NVIDIA Quadro FX 4600 graphics card $2,000+ & video cards are well known to interfere with other PCI hardware for mysterious reasons).  
 
My solution was the cheapest since the MOTU PCIe card was $295 and the video card was $2,000.    
 
I post this in the interest of connecting particular hardware together in a manner that's usefull to other users.  It's not a recommendation, and it may be possible that users of other motherboards won't have this problem. 
Incidentally I'm the guy that does the hardware mods to the Kurzweil 1000 series.  I've got a good handle on hardware, with scopes, EEPROM burners, solder suckers, VOM, and the rest in the shop.  www.k1000.net   AKA Alzerom - David Brown of course just like my name here is my user name.   
Perhaps that explains the background better?  

I would like to hear the outcome, please post results.  I have had a few mysterious crashes, blue screens.. etc.  about once a week. Video card investigations may be in order.  awaiting MorlboroMan23's results.