There's IDEfix hardware for the A4000, too. But it's still a hack. You need the IDEfix software running in order to use the second IDE channel and it will still run at the same slow speed.
In order to get a real benefit, you should go for a real two-channel IDE controller like the FastATA4000 (= PowerflyerGold).
Best solution would be a DMA SCSI controller like on the CyberstormMK3 or PPC. You can have up to 15 drives on there and with a SCSIDE-Adapter you can also use an IDE drive. On the SCSI controller drives would run at top speed without CPU load.
Lastly, can a GVT-1000 scan upconverter allow my A4000 to hook up to a multisynch monitor and use most if not all the software I have on hand? How about the TVone AVT-3340?
Don't know what you mean by "GVT-1000". All I found with Google was about gigabit ethernet connections. This has nothing to do with video.
As it seems the AVT-3340 only has Composite and Y/C inputs, but no RGB. So you still need a TV modulator which means a huge quality loss. You should rather use a real Amiga scandoubler.
Another solution would be to connect the Amiga to an LCD TV with a Scart cable, provided that the TV has a full-featured Scart connector (e.g. supports RGB input).
Bye,
Thomas