I have a similar issue - I too am running Gearbox on a Dell, Windows 7 laptop.
I'm not running Cubase, but my dropped sound signal is also happening.
I'm playing a 29-minute Backing track on my Laptop at the same time I'm running Gearbox.
I have a USB (2.0) cable connected to my Pod X3 Live.
Gearbox accurately syncs up with, and reflects the patches on my Line 6 hardware.
I can easily tweak and save patch changes, so basic functionality seems to work 99% of the time.
My guitar and headphones are plugged directly into my Pod x3 Live, and I'm jamming along with the backing track, who's sound output is playing thru the headphones - thru the USB cable connection.
As I'm jamming, I tweak the sounds of my active patch in the Gearbox software that's running on the Laptop.
PROBLEM: At some point within 30 min, while the music is progressing on the Laptop, the sound just stops? Everything else seems to still be functioning, except no sound.
Since your observing a similar sound signal loss ...
I'm now starting to think it's something in the Windows 7 setup that might be causing it ... possibly a POWER profile that starts to turn off features/functionality to conserve battery power (even though The Laptops plugged in to AC)?
You indicated that in time, your signal restarts.
Mine, however, doesn't (or at least I'm not patient enough to wait it out and see if it comes back). If I remove the USB connector from the Laptop, in a second or two, you hear the audible response from the laptop that it dropped a USB connection. When I plug the cable back in, you hear the reconnect sound from the Laptop and the playing music's output signal is immediately available again in the audio out signal to my headphones.
So, while I can't directly help answer what's happening with your setup, just knowing you have the same loss signal symptom - now points me to either a unique USB driver problem OR a power profile that's impacting the USB OR sound card, OR (now that I think about it,) possibly an outdated Sound card driver???
I'll check first for a sound card driver at Dell ...
