I was just saying that a USB interface wouldn't be my preference. I have no experience with Window 7 or 64 bit. I'm using Win XP Pro 32 bit myself, with my trusty Ol' Aardvark Q10's & Aark 24 cards.
Being an entirely new computer, I'd wonder about hardware conflicts, so I'd try to find out from Zoom what they might be. Besides your basic Cubase set up, which there may be differences between versions, if you have everything set up properly...

... your VST inputs/outputs, buffer & latency settings, midi input/outputs, etc, etc...I would tend to suspect Windows 7 64 bit as being the culprit.
But then, if you're attempting to run your old 32 bit VSTi's within a 64 bit envirenment, and not doing the proper method to make that possible - a wrapper of some kind I believe - then that may be a problem. Some VSTi's just don't want to play within this wrapper...so I hear. If this is a possibility, then I'd test it with the included Cubase 6 VSTi's only for now.
I'd also be scouring the Zoom R16/R24 forums where there are people who are using these units, and are bound to be Win 7 64 bit users...though not neccessarily flooded with Cubase users. I did see a user here some weeks back who is also using.a Zoom.R16/R24, maybe do a search here.