I've had the 2nd Gen 18i20 USB for about a year.   Really like it, and have not experienced one issue with it in either Sonar or Cubase. 

Thanks Husker. Another vote of confidence.

JohnKenn
Here are a couple links to the PCIex to PCI adapters. One got a negative review because the old card didn't fit, but this is a given and why a minor adjustment to the case with a hacksaw is necessary. Nothing noted on how well they work. Don't cost that much. Could be worth a try to hang onto what already works well.
 
https://www.neweggbusiness.com/Product/Product.aspx?Item=9SIV10D7167649&nm_mc=KNC-GoogleBizMKPL-PC&cm_mmc=KNC-GoogleBizMKPL-PC-_-pla-_-Add-On+Cards-_-9SIV10D7167649&gclid=EAIaIQobChMI3vnGlpfe3AIVibfsCh1dSgd_EAQYBSABEgJYyvD_BwE&gclsrc=aw.ds
 
https://www.walmart.com/ip/Startech-com-PEX1PCI1-PCI-Express-to-PCI-Adapter-Card/13216248?wmlspartner=wlpa&selectedSellerId=0&adid=22222222227000296254&wl0=&wl1=g&wl2=c&wl3=42534089072&wl4=pla-81190916672&wl5=9033014&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=online&wl12=13216248&wl13=&veh=sem
 
Stickman, please update on how the 6i6 works for you.

 
John -
Thanks for this. I followed up and did some additional research. Bottom line: I have some hardware coming my way: A new DAW; a Focusrite 6i6 ; and a PCIe-PCI adaptor card. The Echo Layla 3G has a very small PCB and I'm optimistic that the adapter will work out, albeit with some trimming of the PCI card's back plate I imagine.


For what it's worth, my real-world normal operation with the Echo on my current DAW is ~6ms each way with 256 buffers, for a total RTL of 13 ms. 

I won't side-line this thread further. I think I'll start a separate thread about testing and comparing both audio interfaces in the new box when they arrive. 
 
Cheers

USB2 should be fine for audio usage, and the only reason I went with FW was to have a "dedicated pathway" which wouldn't have a conflicting device in the machine at that time. My only concern for you is the viability of a PCI to PCIex converter.

That said, I did get a FW card for my new machine which required me to back out to MixControl 3.4 (due to Win10, not the card itself). My recommendation would be to ask Focusrite directly about recommendations. They are responsive and can give suggestions on your situation. With any luck they will already know the answer for you.

Wondering also about what if any compromises are there in the PCI conversion. Irony is that some of the old PCI cards are so rock solid and could go on for years of service if the slot itself hadn't become obsolete when you upgrade the computer and the thing will no longer fit.
When I get bummed out about my M-Audio card, I think of the guys who spent 5000 dollars on an RME card.
 
Got a Focusrite box coming that should do the job. Very much interested to get Stickman's report on the PCI converter. There may still be hope for vintage hardware if the converter works as advertised.
John

Report back from the trenches...
 
The Focusrite Scarlett arrived today. Got it up and running after a few glitches trying to figure out the control panel that was bleeding unprocessed signal into Reaper.
 
The unit is excellent. Blows away my old M-Audio hard wire card although the card limited by older PCI slot limitations. Blows away the PreSonus AudioBox2VSL regarding latency and buffer size.
 
Happy camper so far. Leap of faith being paranoid of USB capability, but good advice here prevailed.
 
Thanks also to Jim who many many threads ago gave an argument, supported with data about the relevancy still of a USB 2 connection.
 
John
 

It may be a moot point now, but if anyone is still looking (especially if lowest possible round-trip latency is a priority), check out the Presonus Quantum.
 
Can take the ASIO buffer size down to 16-samples (sub 2ms total round-trip latency).
 
It's a Thunderbolt audio interface, so you'll need a Thunderbolt-3 connection.

I have the 2nd gen 18i8 no issues here. I got a good price on it. Has worked well.

I have some results, comparing my PCI-based ECHO Layla 3G with the Focusrite 6i6 USB 2.0.
For the full story, read here.  To save you navigating my lengthy prose, here is the bottom line:
 
Interface: ECHO Layla 3G PCI
Buffer Size ASIO Reported RTL     Measured RTL
----------- --------------------- ------------
  256       13.7 ms  602 samples    0.015 sec
  128        7.8 ms  346 samples    0.010 sec
   64        4.9 ms  218 samples    0.007 sec

Interface: Focusrite Scarlett 6i6 USB2.0
Buffer Size ASIO Reported RTL     Measured RTL
----------- --------------------- ------------
256         25.5 ms 1102 samples    0.037 sec
128         13.1 ms  578 samples    0.020 sec
64           8.2 ms  362 samples    0.013 sec
 
So, on this computer at least, the Focusrite USB is about twice as slow as the ECHO PCI.

Interesting comparison and will have to check out the speed of the Focusrite on my old Vostro 400 where the 1010LT is receding into dust.
Performance of the Focusrite on the i5 is far better than the 1010LT, but obviously because the Vostro is so underpowered. Good article.
 
Also thanks for your report on the Dim-Pro authorization problem since had the same dead end and thus there may still be hope.
 
John