Different number of digits with same beginning

[phadobas]

So, here is the scenario:
IPS 2000 connected to ICS2400 with CCIS. Here I need help programming the IPS. Originally it was set up as follows:

Leading digit 1 - route to LCR for outgoing calls via telco T1
Leading digits 2,3,4,5,6 - access code to CCIS to the 2400
Leading digits 7,8 are 5 digit extensions within the IPS

NOW:
Got a new phone system (sv8500) which has 6 digit extensions. It is CCIS connected to the 2400.

So now, if I dial from the IPS 2000, I can dial outside by dialing 1 as a starting digit.

With digits 2,3,4,5,6 I can dial into the 2400, but I may need to reach an extension on the SV8500, in which case I need to send 6 digits to the ICS2400 so it can decide to connect my call over to the sv8500. So a number starting with 2,3,4,5,6 may be 5 or 6 digit long depending 2nd or 3rd digit.

So, how do I break these out? Where do I define the maximum necessary digits based on the leading digits? Just spent a whole day doing this on the 2400 and works fine now, But still have the IPS 2000 to set up with this.

Thanks for the help.