I seem to remember on the PS1 that Tomb Raider 3 had echo etc, I've been playing the GOG.com version of TR3 and there are no EAX effects - is this just how the PC port was originally or do I need to set up Creative ALchemy (I use an X-Fi soundcard)? Or is there a setting to toggle in the config files?

Nope, Tomb Raider 3 does not support EAX on the PC. The first PC Tomb Raider game to support it is Angel of Darkness.

The PS1 on the other hand indeed does have reverb processing and while I haven't played TR3 on the PS1 I am pretty sure it supports it as you say it does. I remember Crash Bandicoot had similar effects.

I see. I thought it might be because the game uses the DirectSound API which my Creative soundcard doesn't support.

If you have a Creative sound card, you can use "Creative ALchemy! You can download it for free and it´s very handy for a lot of older games.