I recently bought a new audio interface. My beloved Konnekt 48 had died after 10 years caused by a DC spike problem that affected FireWire port and one of the mic preamplifier.
So I decided to switch. I have chosen MOTU AVB 8M. This because of very good audio performances (123db) and for the price (€1390 while RME UFX is € 2700). The other feature was the possibility to operate both in a USB and Thunderbolt mode. I excluded Focusrite Clarett series because of their unique thunderbolt port. I'm a Cakewalk user until 1996 and I don't want to switch so my question: I would like to build up a PC desktop with a thunderbolt port and so I'm asking you any advice or experience in this direction.
I think to go to INTEL I7 because I'd like to use it for years (the last is working for about 10 years, hardly and flawless until now, when the AMD chipset said "I don't want to work with MOTU" .... Continuos blue screens when MOTU driver switches on).
By the other hand MOTU works perfectly on a I3 asus notebook. MOTU says "no problem with AMD but my PC says NO!
What's your opinions?

AMD are in a bit of a sticky wicket really. Certain propriety technologies are owned by Intel, so they have to create their own version of it and call it something else. Then Thunderbolt was partly developed with Apple bringing new problems.
 
If you are going to be using Thunderbolt and Intel then look at the processor and how many devices you are going to be using. Which RAM and how much you will need. Intel have basically split this into two parts of market, cheap motherboards really only benefit from their cheaper processors and vice versa.
 
AMD have two options, Threadripper and Ryzen 3/5/7 which are 2 slightly different platforms. Threadripper is essentially 2 zen cores stuck together. It will cost around a grand, although there is no sign of thunderbolt support even through 3rd party PCI-E add-ons.  Universal Audio do a Thunderbolt 3-2 conversion card I know of.
 
This reminds me of the Firewire issue where some vendors would opt for Via and others Texas Instruments. The TI was vastly supported whereas the Via essentially was c*** for support. 
 
There's a guy on here who builds music daws for a living.

If you want to run the MOTU 8M via Thunderbolt, you have no choice but to use Intel.
 
Ryzen and Threadripper are good performers...
But to reap maximum performance with low-latency audio, you need to run fast RAM.  
Most X370 motherboards won't even post with RAM settings above 2666MHz.
Gigabyte boards were the least flaky... but still not rock-solid.
We could get RAM running at 3200MHz.  
Once, there was a hiccup that required all RAM to be removed AND the BIOS reset... to get the machine to a working/posting state.
If you're tech savvy, you can work thru these types of obstacles.  
Many folks just don't want to deal with the hassle.
 
If you go with the latest Intel socket 2066 (X299 motherboards), you have to go all the way to the top 7900x CPU ($1000) to get more than 28 PCIe lanes.  The 7900x provides 44 PCIe lanes.  
The mid-tier 7820x provies 28 PCIe lanes.
If it's a simple build, 28 PCIe lanes is fine.
If it's a complex build (say with multiple PCIe x4 SSDs), 28 PCIe lanes is limiting.
If you go socket 2066, Gigabyte and Asus have Thunderbolt-3 available via optional AIC (add-in-card).
The Gigabyte Thunderbolt-3 AIC is hard to source.
The Asus Thunderbolt-3 AIC is readily available.
 
Though not the absolute latest thing, socket 2011-3 (X99 motherboards) is still very fast and absolutely rock-solid.
The 6850k is an excellent performer... and provides 40 PCIe lanes.
You can find numerous motherboards with Thunderbolt-3.
If you're making heavy use of virtual instruments, socket 2011-3 is a great platform.
 
NOTE:
Don't assume that because a motherboard has USB-C port/s that it has Thunderbolt-3.
USB-C can carry USB-3.1 or Thunderbolt-3.
Had a guy call last week... and was actually arguing with me saying that Gigabyte had X299 motherboards (actually available) with Thunderbolt-3 on the motherboard.  This is not correct.  
Gigabyte X299 motherboards have a USB-C port... but it's carrying USB-3.1.
Gigabyte X299 motherboards can provide Thunderbolt-3 via an optional (not included) Thunderbolt-3 add-in-card.
 
 

Thank you Jim.
Absolutely perfect!
This is the start point.

Very concise and useful. 
 

Jim, can you give some insight on what PCI lanes are actually used for? I know a video card can use up to 16 but that seems unlikely to be necessary for a DAW system. And the NVMe disks use 4 I think? Struggling to see how 28 lanes would be limiting even with a seemingly excessive 5 of those. But that just means I must be missing something.

Here is something that is not always speculated. When SLI/Crossfire is used on a system sometimes the lanes are split in bandwidth. For example, two PCI-Ex3 Graphic cards might use x8 speed each rather than x16 each. Meaning they are use in tandem rather than double the speed as you would expect.
 
From what I have gathered from reading some motherboard manuals, the use of NVME can disable certain lanes in a motherboard chipset. So obviously for a maximum coverage you want a processor and chipset which gives you a larger range of options.
 
It is the same regardless of Intel and AMD in some cases, so before you buy do your homework.
 

Sanderxpander
Jim, can you give some insight on what PCI lanes are actually used for? I know a video card can use up to 16 but that seems unlikely to be necessary for a DAW system. And the NVMe disks use 4 I think? Struggling to see how 28 lanes would be limiting even with a seemingly excessive 5 of those. But that just means I must be missing something.

ALL PCIe hardware uses PCIe lane/s.
The latest generation of SSDs (U.2, M.2, and PCIe) each uses 4 PCIe lanes.
The newest USB-3.1 controllers are PCIe Gen3 x4 (4 PCIe lanes).
Whenever you see a peripheral with PCIe x16, that means it uses 16 PCIe lanes.
 
Let's use a new Skylake Extreme 7820x as an example (provides 28 PCIe lanes):
Your video card will use 16 PCIe lanes.
That leaves 12.
Now let's say you want to run two PCIe x4 SSDs.
You're down to 4 PCIe lanes for all remaining peripherals.
 
If your build stops there, you're likely fine.  But sometimes it's not that simple.  
ie: If you're running a CPU with 28 PCIe lanes, some M.2 Ultra (PCIe x4) controllers will be scaled back to x2.
The motherboard manufacturers don't always put this useful tidbit in their manuals.  
So... the SSD that's capable of sustaining 3200MB/Sec will yield 1600MB/Sec.
In this example, the workaround is to put the M.2 Ultra SSD on a PCIe adapter card... and put it into a full-length slot where it has the necessary 4 PCIe lanes.
 
On a simpler build, it's a moot point.  
On a build where you want to leverage massive bandwidth, 28 PCIe lanes is limiting.
 
Getting outside the "Audio/DAW" realm, if you're running a pair of video cards, 28 PCIe lanes is extremely limiting.
 
 
 
 

That's true, but I was thinking specifically along the lines of "why would I ever run two videocards in a DAW". Add to that that not every videocard actually takes advantage of x16, e.g. my next-to-last-gen GTX 980 does fine with x8. Many people even use on board video.

It depends on the build.
The more complex, the greater the limitation of 28 PCIe lanes.  
 
Many folks (even if they don't specialize in video) now straddle the line between audio/video production.
Working occasionally editing/rendering video...
These folks aren't going to want to drop their video card from 16x to 8x.
 
I mentioned the new X299 motherboards have three M.2 Ultra slots, U.2, USB-3.1... all of which use 4 PCIe lanes.
If you're running multiple higher-bandwidth peripherals, you can plow thru 28 PCIe lanes.
If your build is relatively simple, you'll do absolutely fine with 28 PCIe lanes.
 
Intel made an odd choice by limiting the 7820x ($600) to 28 PCIe lanes.
Most folks (wanting that level of machine) aren't typically looking for a simple 3-drive build.
They're pushing the limits of the hardware... some running 8-12 SSDs.
These folks are forced to go with the 7900x... especially if they want to leave options available.