First thing to try is nothing. I've lost count on the times something hasn't worked, come back to it next weekend and its fixed itself!?

I'm guessing you've tried both in a different PC? Maybe its the motherboard being funny? or maybe simply moving everything around kicks them back to life?

The two AWE64 Golds are hopeless. I tried them in other machines, and other cards work correctly in that machine. For the Ti4600, I haven't tried it yet in another machine, but a ti4200 is perfectly working in the same machine right now. 😢

Let's see what will happen next week...

Just a thought on the AWE64 that became "invisible" - had this happen to a friend's SB Audigy, back in 2003 or so. Card disappeared from Windows, official Creative drivers wouldn't install (no Creative Soundblaster hardware found, or something along this line). The card worked with the KX drivers, but my friend needed the functions offered by the official drivers (SoundFonts I guess), so the card went to the store where he bought it for warranty. After a while they said they couldn't reproduce the fault and gave him back the card, useless as before. I searched the net, and found out he wasn't the only one with this problem: apparently the content of a small EEPROM from the board gets corrupted for whatever reason, in combination with certain other hardware (motherboard, chipset, bios, dunno).
I found a russian site/forum where they had dumps of a few Creative card EEPROMs, along with a schematic for a crude, parallel-port programmer and the needed software. Unsoldered the chip from the board, built the programmer, the chip was completely blanked (all FF or zeros, can't remember). Burned the correct code for that card, but as a measure of precaution i soldered back another EEPROM, this time in DIP package (to make reprogramming easier in case it gets corrupted again). The board worked perfectly after that, and it might still be in service 😀

Looking at my AWE64 Gold, I see at least one such chip (93C66)...