asterisk users - Feb 2004 - X100P analogue cards and impedance matching

Hi -

I have looked but can't find details of the impedance that the analogue 
  PSTN interface card X100P presents.  Am I right in assuming it is a 
resistive 600 ohm match?  If so, is there anything I can do (in software 
or hardware?!) to 'tweak' its impedence to the complex impedence 
normally presented by a UK phone line?

The reason I ask is that old chestnut - echo...and I wonder whether 
resolving the impedence match might overcome some of the echo issues.

Rgds
Tim Robinson
Basingstoke, UK