I think I've found a way to play MAX2 multiplayer online using modern systems.
I haven't actually tested it yet, but it looks very promising.
Basically it involves emulating a serial port connection using a program called TCP-Com.
This tutorial shows the basics of it:
http://www.youtube.com/watch?v=O9RXxWhgVVo
Although the tutorial is for Diablo, I'm sure the same thing can be applied to MAX2. Also, the guide involves downloading Tunngle, which is a program that's simliar to hamachi, but is more geared for playing games, and generally works much better. However, you could probably apply the same method to hamachi, or even just using a direct connection.
Let me know if anyone's tried it!

Just discovered: you could probably play MAX2 with more players and less fuss by using IPXWrapper, an open-source IPX wrapper.
Download the latest zip file from here: http://www.solemnwarning.net/ipxwrapper/ and then move all the .dll files into the same folder as MAX2. Haven't tried this, but for those who are looking to try and play this game multiplayer, give it a try! And post here if it worked or not :)