Echo Layla 3G vs. PCIe Bus

I'm trying to help a friend get started on Sonar X3e Pro. He has a hand-me-down Layla 3G interface and a Yamaha CP-4 Stage piano to use as a controller. The PC is a custom built i7, 7200 rpm drives, lots of RAM, Win7 64-bit. He has installed the latest drivers from Echo. He seems to have it all connected properly, because he is getting both analog sound out of the Yamaha and audio from soft synths controlled by the Yamaha. But when using soft synths he tells me he gets a lot of crackling, distortion and dropouts while playing, making the system unusable.
 
I have been reading on this forum that Layla was designed for the old PCI bus and never updated, and some Sonar users have had problems making it work with the modern PCIe bus. So I'm wondering if anyone who has experience with this can shed any light on what might be going on. At this stage replacing the motherboard is not an option, even if there are any available with old-style PCI slots. And though at this time he doesn't really need all the I/O capability of the Layla, why give it up for a slower (USB), less capable box if he doesn't have to?
 
Are there driver settings or a workaround for this that anyone knows of? Or does my long-distance diagnosis seem wrong? If he can get the Layla working reliably on the existing PC that's the way he wants to go.  I should mention that money is an object, as usual.
 
Thanks for reading!
 
PS: There seems to be no existing Sonar instrument definition for the Yamaha CP-4. Could this have a bearing on the problem?

Thanks Sven, that's good to know. Wish it were that easy, but this Layla is not working so far.

Thank you for this input, Jim. I may get a chance to sit down at my friend's PC in the coming week, and I'll see if I can figure out where "CPU throttling" lives in the BIOS.