What memory cards did you used for the iFlash?
Oh, I thought I included that info...
Two of these:
https://www.amazon.ca/gp/product/B08L87V4PH/
If it were me, at that point I'd open it up again, and either reformat the cards in a card-reader before trying again, or just give up and put that iflash and cards in a 7.5gen and try with a 128gb card in that 6th gen.
The whole idea of doing this in the first place was to have *my* old iPod upgraded to a nifty terapod. The person who did the work for me (and they did not charge me for the work, they just have a passion for this sort of thing) assured me it was reliably upgradeable with these parts, but from what y'all are telling me it's not. So now I'm supposed to go out and source another iPod, tear both of them apart in the hope I don't destroy them (or myself), and hope against all experience to contrary that it will all work? With all due respect, at that point it's far cheaper and less stressful to buy a new player that I don't have to torture myself endlessly to have working. Like I should have done in the first place, in hindsight.
[EDIT] actually, thinking about it, I'm not entirely sure it is supposed to show up as a drive (as opposed to just a 'device') when it's in DFU mode. Can't actually remember (and can't check because I'm in the middle of syncing an ipod). The idea is to restore it with iTunes at that point, as iTunes should say it's found an ipod in recovery mode.
As for DFU mode, when I did the last rebuild with the Dev Build, that was the *only* way that I could finally it recognized as a disc so that I could reformat and then get the Rockbox Utility to see the mountpoint. Either way, it doesn't see it as a disc now in *any* mode. iTunes is useless as well, it recognizes the iPod but when it tries to start any recovery it goes to the nameless error 1675.
I was interested about disconnecting the battery cable, so I wondering if letting the battery completely drain might not achieve the same effect. Otherwise, I'm rapidly approaching 'cut bait' time, despite the time and money invested.