Use Xplorer360 beta 6 instead of Action Replay. Make sure you use the Krayzie 1.1.1 gamesave softmod installer. Copy the numbered folders (5553000c and 21585554) to the root of your memory card.
Make sure your current Microsoft dash is version 5960. If not, use a newer (post 2004) live-enabled game to update the dash - Halo 2 and Doom 3 definitely work - I've used them both - and Pro Evolution Soccer 4, Need For Speed Most Wanted, and Goldeneye Rogue Agent should also work. Just load the game, select the option to play on live, and the first thing the game will do is update the dash. You don't need a live account, or even a network connection. With Halo 2 you just select "Register New Account", and it's similarly obvious for Doom - and I'm sure for the others as well.
Once the dash is at 5960 you copy the gamesaves from the memory card to your Xbox using the Xbox dash. Run Splinter Cell, load the gamesave, select "basic install - UnleashX dashboard, and follow the instructions.