Now that I've read your other post, I'm even more confused. Are there two 1800Ts (a 320GB and a 500GB) AND an external 500GB disk?
Ha!
Sorry...
I had a HDR-1800T 320GB and copied files from it to an external 1TB USB drive.
I then got a HDR-1800T 500GB and used the same external drive - all existing SD files on the external drive were happily played back on this newer Humax (I deleted the few unplayable HD files).
I then recorded and copied onto the external 1TB drive with the newer Humax HDR-1800T 500GB, no problems.
Now the newer Humax HDR-1800T 500GB has died (probably), I have dug out my original Humax HDR-1800T 320GB. It can play ALL the files on the external 1TB USB disk, no problems.
As I like to have backups for files AND the hardware that can play them; I have been unsuccessfully looking to get another 1800T for a few months.
But I have now spotted a 2000T that looks promising, hence my original query as to compatibility.
From your original reply, and looking at how similar (identical!) the 1800T and 2000T back panels are, I am 95% sure that the 2000T will be as happy with the external drive as both my 1800Ts have been.