The toaster must be fed broadcast quality video. The definition of broadcast means the timing must be spot on. At the time NewTek engineered the toaster including TBC chips would have been too expensive.
I had similar problems. I used to feed input 1 with a live DV cam, input 2 with the composite out from a Cable box. For what it's worth you can feed the toaster with a DV camera off of tape.
Also there are external modern TBC's that you can purchase from B and H photo. I did this with one of my flyers.
Gotta understand the way the toaster was meant to be used:
A) Live production- 4 live cameras, calibrated and synced
B) A-B roll edit system using the same PRO VERSION BETACAMSP make and model VCR
I think you're trying a plug and play approach used on some PC consumer gear. If you run that output through a vectorsope it would be a mess. The toaster output was designed to be top notch and pass the inspection of old Skool TV engineers.
Another solution for me was to use a firewire router with 4 inputs, connect my DV tape sources to that. So I had 2 sony cameras, a DV tape deck, any analog sources were run through that with a Dazzle Analog to DV bridge. I connected this firewire router through a MAC using Imovie and would switch the sources.
Pretty ghetto solution but i was able to maitain sync.
Also helps to calibrate the toaster with the inputs you intend to use, once you start plugging and unplugging sources you cause problems.