Part of the issue with NAS is that you really need to keep capture systems off the network, especially older OS that are easily defeated by modern malware. Unless the entire network is air gapped, not online. System activity, including network activity, is not good for capture system.
Those who have basements, or usable attics, are so lucky. Nothing like that can exist here. Jealous!
There is a single PCI AIW that is not crap, and it's rare. It's not something you'll find on
eBay, etc. It took me years to acquire mine. In fact, I acquired more than I needed, and I've since sold off some of the spares. (I may still have a spare left.) It's not as simple as looking for the Theatre chips either.
TBSC is vastly better than anything Creative has ever made. The audio on all Creative cards is tinny, compressed sounding. It's not rich. And no, this is NOT from an audiophile perspective, those people are nuts. When you realize VHS audio is already degraded, it doesn't take much to make it vastly worse. So while some audio test pattern may be fine, or a music CD, or whatever, it's the actual VHS>digital usage that matters here.
I'm busy lately, getting to PMs as time allows.
Overlay mode has never been stable. If preview is fine, use preview. It's always been the safe mode. Some cards cannot use overlay at all, while others are indeed "twitchy". This can be repeated with lots of cards. I don't see how it's even possible to be caused by a TBC, though I'd not rule out other conflicts. It's why my workflows are tested as workflow, to remove as many external variables as possible. When you buy gear piece by piece, sometimes you'll notice oddities. When you baseline test gear, using AIW, use MMC for the preview. Fall back to
VirtualDub later, for the actual use.
VirtualDub can be a misbehaving variable at times. If you see issues in MMC as well, and know the item is fine (as is the case here), then infamous AIW drivers may be fluky. Upgrading drivers is actually rarely the fix, rolling back to stable is.
Overclocking for fun? Sure, why not. Go for it.
For me, the "fun" of playing wore off years ago, because I started to view them as just the dumb tools they are. My desktop is about as exciting as the toaster. Though I do enjoy my battery Greenworks leaf blower!