I forget all the names of the products, but you went from the WinTV PCI to the WinTV PVR 350 (something like that at least). The chips on the 350 card are probably better, you likely gained more than s-video, but an overall better card (the 350 also has the coax tuner that the 250 lacks). www.shspvr.com
keeps up to date on Hauppauge and PVR products. These are good cards, and I suggest them. Using proper MPEG settings, and feeding it a clean signal, will get you good results.
The AVT-8710 was a good choice. I actually have a TBC-1000 and a couple proc amps, but the 8710 is a decent TBC and basic proc amp all in one unit. You should like it. One of the 2 TBCs I recommend.
The Canopus ADVC-100 is not a unit I find overly wonderful. There are two audience for this:
1) Most people have trouble at converting video, and this is a really dummy-friendly DV unit, and has few errors when being used. They love the device and are reasonably happy with the quality they get from it.
2) Serious videographers have a problem with it's compression. It has a major drawback with NTSC video (North America video) in that color is overly compressed to a DV 4:1:1, whereas DVD is 4:2:0 and tv is 4:2:2 (the middle number is most important). This tends to butcher the color of VHS tapes. DV is a decent format for video cameras, but not really for converting analog signals. Uncompressed or at least 4:2:2 max compression is preferred over 4:1:1. It also has a tendency to darken the video.
The trick with the ADVC is to convert a VHS tape. Notice how it treats red and green. You'll see artifacts especially on neon colors, laser beams, things like that. If you enjoy the quality, keep it. If not, this is why.
AVI (like DV-AVI, the format of DV) is preferred for advanced editing, so this may be a decent companion for your 350 card.
12MB/s for MPEG capture is not only overkill, but outside DVD spec (max 10.08 including AC3 audio). Find the BITRATE graphs on the bottom half of this page: (http://www.digitalfaq.com/capture/avivsmpeg.htm
The Philips DVDR80 recorder is not one of my favorites, but it can provide quite adequate quality, especially in 2-hour mode.
That said, however, I would not export the MPEG file to the recorder, as it is then re-recording and therefore re-encoding an already compressed MPEG signal. That is not good. You would be better off authoring a DVD on the PC and then recording the authored video to a DVD burner in the computer.
I think you've got some extra steps in there that are not needed. Go to this page to see a quick run-down of my processes: www.digitalfaq.com/digitalfaqway.htm