Here is a snip of what I guess is the issue and what they are aiming at from Universal Audio..
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We haven't put together a full compatibility matrix for Opteron and Athlon-64 chipsets yet, however we have some preliminary information that can be useful for selecting system configurations. The chipsets available for the Opteron and Athlon-64 include the AMD-8131 (PCI/PCI-X), AMD-8111 (PCI), VIA K8T800 (PCI), and nVidia (we haven't tested this yet).
Based on out tests and feedback from our beta testers, the VIA chipset is by far the best available. It performs extremely well, and several on-line comparison reports have shown that Opteron and Athlon-64 systems using it perform very well. The AMD-8131 works, but it requires setting the AMD-8131 mode in the UAD-1 Meter, which improves UAD-1 DSP performance, but reduces host CPU performance because of issues with this chip's PCI bus arbitration logic. The UAD-1 works well with the AMD-8111, but some systems using this chip along with the AMD-8151 AGP controller do not. The Asus S2875 uses this configuration.
Based on preliminary reports on some of the Asus boards, we currently don't recommend them for use as DAWs because the system architecture is not designed for low-latency media processing (most are designed as servers, which are not suitable for use as DAWs for many reasons).
Based on our initial analysis, our position is that some HyperTransport-based systems have been released too soon, while others are generally not suitable for use as DAWs with or without the UAD-1. The problems are not due to HyperTransport or the AMD 64-bit processors, but rather the system chipsets and system bus architecture.
For trouble-free operation and best performance, we strongly recommend using the VIA K8T800 chipset, as this has demonstrated both superb performance in all applications, and is the benchmark with which all other HyperTransport chipsets should be measured.
For optimal DAW performance, regardless of system type, we recommend putting audio devices on their own PCI bus segment to avoid audio performance degradation. Since most high-performance systems typically have multiple PCI segments, this can be done easily. Keep in mind that nearly *all* peripheral devices in the computer are connected to the system using PCI (which stands for Peripheral Component Interconnect), either using internal PCI segments within a chipset, or sharing external PCI segments with the PCI slots. The best systems have multiple PCI segments to isolate performance bottlenecks.
For analyzing Windows systems, we recomemend using SiSoft's Sandra performance analysis software. This is available as a free download at
http://www.sisoftware.net . For people insterested in full PCI system analysis, including bus topology and IRQ routing and sharing, we recommend using ApSoft's PCIScope, a 14-day demo version is available on-line at
http://www.tssc.de .
Regardless of bus bandwidth and clock/memory speeds, the system chipset's I/O queue depth largely defines system performance. The more I/O segments there are in a chipset (memory, AGP, PCI, etc.), the higher this number needs to be to avoid delays caused by data transfers blocking each other.
Finally, it's very important to remember that the amount of money spent on a system has little to do with how well it will perform as a DAW. It's very easy to spend several thousands of dollars on a backbone server platform that will perform terribly as a DAW.
