I dont get how all this tech talk comes into play. Wouldn't it seem logical that you could match halo on coop and split screen. You have a quake engine based game running on a geforce 3 ti, I would expect these things.
quake1 is a really old rendering technology. It's based on a vertical scanline software rasterizer that Michael Abrash wrote for the Pentium (1!) chipset. The 3D version of that rasterizer (which came a year later and was written for Rendition Verite and 3Dfx SST1 chipsets) doesn't take advantage of vertex shaders, pixel shaders, vertex buffers, static pushbuffers, or hardware transform and lighting. A half-life engine game like CSX is mostly CPU bound on an xbox, which only has a 600MHz *celeron* CPU.
So you can throw as much video card you want at a half-life engine game; if you're memory and CPU limited, you can't do anything else with it.
So we did some other things to eat up extra fill rate (high dynamic range light bloom, dynamic iris simulation/gamma ramp, detail textures, pixel shader water, etc) that doesn't require extra CPU. Because there's no CPU left, unless the entire engine gets rewritten. On a relatively short development cycle like CSX, there's just not time to do that.
No splitscreen. But you can play 2 players on system link and play coop against bots, or do the same on Live.