Well I got nearly half of them (16 out of 34) transferred to Memory Card, and recorded the runs onto my HDD Recorder. The ones that wouldn't work were all the ones I converted from MAX files. So I guess I don't know how that conversion is supposed to be done. I've done it in the past with some GT3 replays and was able to see the resulting replays, so I'm confused now. I'm using the so-called PS2 Save Builder, opening the MAX file and saving it as a SharkPort2 file (.sps). I also tried saving it as an X-Port file (.xps), and changing the extension to .sps, that's how I'm able to read the NTSC X-Port replays, but still no luck.
So unless/until someone can give me a clue as to how to get SharkPort2 replays out of these MAX files, I'm not able to proceed with the remainder of the runs. Maybe someone with both a MaxDrive and a SharkPort/X-Port can convert them? Hopefully I'm just converting them wrong and the right procedure will solve my problem.