If I use that extension can I de-select stuff so I don't redownload what I already have? It would be a waste of time and bandwidth.
Yep, you had to deselect the 170GB ZIP to begin since it does a total *.zip initially.
What I checked for you is a problem though: in Settings, there's only 2 options for what to do if a file already exists in the target folder, Rename or Overwrite... There should've been one more like most FTP apps provide, a Skip, but oh well. So yeah, you'll have to manually deselect lots of files to speed things up.
You should be able to get the hang of it in ~5-10 minutes, but the other caveat is it doesn't let you set a target download folder, you must change that in FireFox General settings to the PC Engine folder you have your other files in. That's about it.
Results: I started the downloads at ~10:00pm last night and all 490 archives finished today at 8pm on a 100Mbps cable line.
I was meaning to find a source like this eventually given the ROMpocalypse Nintendo triggered which made me nervous as ROM sites started "bending a knee" by abandoning non-Nintendo games also after those lawsuits went out!
An aside, it'd be an interesting project to switch to a lossless audio compression format like FLAC/APE and use some other tricks I thought of over the years: Make a diff file with the PCECD data track 2 and its final backup track, then during extraction, just duplicate track 2 and run the diff to recreate a 100% copy... You could achieve even more compression by not carrying both data tracks, but the archive would need a batch file to decompress.
At least 40% of 170GB could be knocked off or more while still preserving data 100%. But, it's probably not really in demand of an idea and I'd have to see how to upload back to WayBack like they did. You'd need batch files for other OSes besides Windows too, like Linux, Android, so another complication...
These archives are ready to mount/burn/work as-is on Windows, Linux, Mac, elsewhere. Probably the Terraonion add-on scans the ZIP for a CUE file, gets to work, all without manual decompression too! That ease is more valuable to most people than space-saving hacks!
Hmm, doesn't seem like you're trolling me, so in that case, hello, fellow PCE turbro...