Whoever said there is a hardware issue with a microprocessor and an audio interface doesn't know what he's talking about. Your processor is abstracted away from hardware. Its the motherboard chipsets that cause problems with audio interfaces, and it is only with cheap Firewire and wi-fi chipsets. You can always just get an aftermarket Firewire card, or use a USB wi-fi adapter. USB works the same on every computer, regardless what type of processor you have, as does Firewire.
There aren't a lot of formal studies on this that I have run across due to a lack of comparable benchmarking tools people in the industry understand. I'm a computer engineer and an audio engineer and I am studying this right now so I'll share what I know right now. With audio, the thing that matters the most for running VSTs is multi-threaded performance, and audio latency.
When the latency is lower, its better for playing keyboards, drums, and using VSTs for tracking effects for vocalists and instrumentalists. But for playing back sequenced audio, latency is not an issue. Lots of DJs perform exceptionally well with horrendous amounts of latency without even realizing its there. Playing drums through a VST on the other hand is another story and the latency is most painful when tracking vocals with a wet monitor mix.
I make professional audio interfaces for a living and the chipset manufacturer that I use, XMOS, use 16-thread 50MHz cores instead of 2 400MHz cores. Multiply 16x50MHz and you get 800MHz, which is the same number of clock cycles as the dual core. By doing this, the audio latency gets cut in half. They have the lowest latency audio interfaces chipsets in the world because of this.
Intel processors are renowned for having excellent single threaded performance. Most video games only take advantage of two threads, which is why Intel crushes AMD for high-end gaming on older games not optimized for parallel computing. For mid-range gaming though, it doesn't matter if you use Intel or AMD, because your GPU is going to be the bottleneck, which is why Microsoft and Sony use AMD processors now. The bottleneck factor is important because it doesn't matter how fast your CPU is if its waiting for the RAM to send it data.
The thing that is good for accelerating multi-threaded computing is L2 and L3 cache. Running lots of VST plugins can cause thousands of threads to be running and they will use up all of your cache, unlike video games. Each time the processor switching from working on one thread to another, and the next thread is not in memory, the CPU stalls because it has to get data from RAM, which takes a long time.
AMD defiantly has a leg up on Intel dollar per dollar because those FX-8xxx series processors have two more megabytes of cache than the Intel i5-4570 Haswell. You'll have to pay an extra $110 for that much at Intel. The Piledriver cores also have more than 3MB more L2 cache than Intel, which translates into higher performance for AMD. AMD's approach with the larger shared L2 cache is a smart way to do it, and contrary to what many Intel fanboys think, is a true dual-core. Intel's hyper-threading isn't really that big of a performance boost, and two cores with shared resources can tag-team threads faster than two threads with a larger shared L3 cache. But the size of the cache only helps you out so much. Smart scheduling of threads around RAM latency can reduce this significantly and there are a bazillion different ways you can teak apples to oranges you have to benchmark it.