Hi same thing.
Update to 2.71 ==> no Sound ... I went crazy 'cause I thought it was my mistake..
Downgrade to 2.70 ==> works perfectly
It looks like the 2.71 is not ok, therefore, why is it not just taken out from the download area or at least having a hint that Helix FX has issues with that 2.71 software version?
By the way, just for support as I was also looking for "how to downgade": I just did that through Line6 Updater, download the software from the page (2.70), run Line6 Updater, chose the software and that's it ...very user friendly!!!