The Interceptor was the "low end" Alien. Retailed only $600, weighed a bit more, etc. The Remains was the $900 high end, under 2 lbs, all the latest and greatest stuff was on it. The Independence can be considered just a drop in replacement for the Remains while the Interceptor line ceased to be.
Milling was different, internals I'm fairly certain were the same. It's been too many years for me to remember for certain that they were or not. The best way to compare, would be the Interceptor is the Ego 10, The Remains is the SLS.
They worked relatively the same. The remains had the integrated lpr housing and the interceptor had a lpr block. I do believe they both ran at the same lpr pressure. The internals for both used the same parts atleast for 06. After that they might have changed.