Alles anzeigenno one will joke here about your issues - we have all had them
I've a late 2013 27" iMac (so think the same), i had issue with 10.8/5.0.6 with the usb 3 ports and resorted to using a usb hub,
but the 5.0.7 build on 10.9 works ok without a hub, but i don't use as a sound card anymore , or cubase - but i did do a test with 5.0.7 as a sound card, and found only core audio worked for me (not bit accurate)
distortion is often caused by incorrect sample rate.
when using the virus as a sound card over usb, your virus should become the clock master, its worth checking on the virus that your audio setting are set to auto.
(they should be automatically with usb).
then on the mac, check audio midi settings and check you are using 44.1khz NOT 48khz, and check in in cubase that this is also set to 44.1khz
(i don't use cubase, but some daws need the clock to be set explicity, others default to the macs sample rate)
other than that, the normal usb things to try… unplug all other usb devices, then try each usb port in turn…. if that doesn't work try using a usb hub.
soundcard - you should not need one, but Ive bought one and prefer it… it gives you more options, and means the usb is not going to be loaded with audio data which is a good thing (especially if you do multi channels, or send audio to the virus e.g. vocoder). also I think (as others do), the audio sound warmer via the analog outputs.
if you do, get a soundcard go for a firewire one (and you will also need a firewire->thunderbolt adapter), otherwise you will have to be very careful with for usb assignment which is no fun with a Virus!!
e.g. I bought a focusrite Sapphire pro 16, but depends upon your needs, in retrospect wish id bought something with a few more input/outputs - as spdif is very flakey on the virus ti (cannot sync to external clock, and spdif input and output are not sync'd properly)
good luck, also of course log an issue with Access support they will try lots of options with you.
(report back here though, its always good to hear what solutions people find!)
Just for your info - i have checked. and everywhere is 44.1 KHZ. The difference was only in 32-bit...and 16 bit in project. BUt the same distorted sound during recording.
So i've lost couple weeks already and still nothing. And i am also surprised on service level of Access. Here is the current topic... and please be patient to solve the issue here. Not only for me.. foe everybody. But - in fact... It os very pity 
Still no result .. with the latest iMac, with the latest OS of Virus and the latest OSX....
Good luck for those whose still struggling...
