I am not sure if what you are proposing would work.If it does not then I would suggest you try the following.
If you have the model Sony 320 that was not purchased in the UK, then your model most likely has what is known as " signal convert function" sometimes called pass-through mode.
This enables you to input an analog video ( from your VHS player) into your Sony 320 and get a digital video out from the Sony FireWire port then to your Mac.
With this set up you may have to import using the Record function in QuickTime Player as iMovie may not recognise the signal, as timecode may not be present.
https://support.apple.com/en-gb/HT201066
Or alternatively if you only have a few VHS tapes then you could try recording these onto Hi8 tape in your Sony cam' and then transfer onto Mac as you did before. This way you may well be able to import into iMovie as against QTP as this method should have the timecode present that iMovie requires.
The procedure for signal convert and for recording onto camcorder tape are in the manual which can be downloaded from the Sony support site. Be sure to set up the Sony cam' menu as directed in the manual for these methods.
Let us know how you get on.