Hi,
It is actually an interesting challenge to get a proper multiplayer experience with more than 16 players if the lowest performance machine is a Pentium 166 with no HW acceleration, most games that targetted that system doesn't have support for more than 8 players. So I would drop the more than 16 players optional requirement if I expect people to show up with systems with that performance rating. The only game that most likely function with proper FPS on that system with that much players running around is QuakeWorld.(As already suggested by @leileilol)
If we drop the requirement to 8 players a lot more choices become available, they have been already mentioned sometimes by multiple people, but my opinion about them :
Jedi Knight - I also have to confirm that it works on a Pentium 166Mhz and it can be a very fun game to play.
Descent II - Haven't actually played with 8 players on a Pentium 166Mhz as the largest Descent II LAN party-s(All 2 of them 😁) I have participated in had only 4 players, but I think it should work.
Red Alert - I remember it working fine.
Total Annihilation - Should work fine if players use normal strategies and tactics in the game, however if multiple players use "zerg rush style" tactics then i think it will overwhelm the slower systems.
The OG WON version of Counter-Strike can be fun but players with the lower end systems might have to accept to score low even if their actual skills are better than the ones using the higher end systems, as they will get lower FPS and resolution than those with a P3-500Mhz equipped with a HW accelerator.
I would recommend bringing multiple games to the party so if one doesn't works out, there will be backup plans to have fun.
Also you used "software acceleration" in your opening post, I know what you mean, but that phrase always brings a smile to my face 😁, when hearing that I always imagine a sales/marketing type saying that when the competition all showed up with HW accelerators in the systems they are trying to sell and the poor marketing guy have to improvise something on the spot to not make his system without a HW acceleration sound bad in regards of the competition 😁.
EDIT: Actually Total Annihilation supports custom unit limits per player, but IIRC you have to edit an INI file to do it and I don't remember the exact name of the configuration variable to set, however you can adjust this to a lower limit and tell players that "mass wave attack" tactics will not be useable, and I think it might be playable that way.
"A process cannot be understood by stopping it. Understanding must move with the flow of the process, must join it and flow with it." - Dune