I have a PBX in NYC with the same Problem 9xxx Are the DIDs and I use ICHT to Convert. So my employess internal EXT are 6xxx and there DID is 9xxx. I simply Del the 1 digit and add the 6, it works well.
1.(service/feature) match the sevice type on page )0ne
2. (call len) I asume are (4)
3.called number) leave blank
4.(del) =1 (it will del from first to last)
5.(insert) (New digit)
rest blank.
Now because you have 2 sets you will have to have a trunk group for each, Hopfully you have 2 T1s that a carrier that can route the 1xxx down one T and the 8xxx down the other, Or (low volume) if you only have one T split it into 2 Trunk groups tg1(1-12) 1g2(13-23) and have the carrier route accordinly. ( like 1xxx tg1 acend 8xxxtg2 decend) or something.
Oh if you want to test it out just Make an 6xxx ext (or whatever) that matches 0ne of your unused 1xxx or 8xxx, and just enter the whole number in the 1xxx (called number feild), then del = 1 and Insert (6), Brige that EXT to your phone and call yourself over the PSTN..should work
Although The above solution will work, I alway prefer doing it right if I can, that in your case requires changing facs and dacs, or getting a new block od DIDs.
good luck.