The A/D buisness is a nasty one for sure. The biggest problem I have is quality vs functionality. However don't fool yourself into thinking this is only a problem for FireWire. It's a problem in the industry for not supporting newer platforms and newer OS's, so either you don't upgrade or you have a several hundred (or thousand) dollar paper weight.
I like PreSonus' hardware and innovation. Dollar for Dollar they have some great deals for the functionality. However their driver support sucks. I'd read somewhere that they outsource their driver support, which would explain why updates take forever, and often times don't work at all.
My long story with my relationship with the AudioBox 18x18VSL, goes back to buying it after talking with a PreSonus Rep. I was really impressed with the Studio Live functionality, and the ability to get EQ, compression, and gating on every channel before recording the signal, that was huge! Especially on my limited budget. However it really sucked when I had to buy a new laptop and discovered their driver was incompatible with the newer Intel USB 3.0 ports. Their advice to me was to plug it into a USB 2.0 port, the only problem being is my laptop had all USB 3.0 ports. That was back in mid 2013, and they only recently resolved the issue. I had since sold the unit and moved to a FocusRite Scarlet 18i20. I love the mic-pre's on this, but to be honest I hate the layout of the thing compared to the PreSonus. I hate having 2 inputs on the front and the remainder on the back, it just makes cabling more difficult and I don't like the look of it. The PreSonus having all the inputs on the front was very convenient for me. The bigger problem was not having the VSL effects, which FocusRite offers nothing like this on USB interfaces.
Since the problem was resolved with the VSL. I bought another 18x18 VSL and use my FocusRite through ADAT. However I worry about what kind of support it will have for Windows 10, since PreSonus is so bad about sustaining their older product lines. And when I say "older", I mean stuff that was introduce 2-3 years ago.