I'm out of town for the next couple of days (and I'm typing this on my phone) so I probably can't go too deep until I get back. But here are some more thoughts.

I haven't used Mac since the early OSX days (PPC era) so I can't really be much help on the Mac side. But I know there are other users here running Mac. Maybe they will chime in.

I don't see any issues with your seq install process. I don't think you need to explicitly set promiscuous mode on the interface, but it also shouldn't hurt anything. You also shouldn't need to use the mapconvert script anymore, but again it shouldn't hurt anything.

It's not yet clear to me if this is a preferences issue, a UI (qt) issue, or a packet/network issue. But maybe we can narrow it down.

I'd be really curious to see what happens if you do a packet capture on the Win box (using winpcap or whatever) from your EQ session start all the way to whenever you start having issue in showeq. Then use seq to play back that capture file and see how it behaves. Even better would be if you could do it with a fresh/throwaway F2P account (so there's no risk to your normal account/characters), and send me a copy of the capture so I can poke at it.