I have the 2006 SX Trail 1 with DHX4.0 rear shock and Marrzochi 66VF up front. Spesialised are sneeky its not a DHX4.0 really it’s a 3.0 ,likewise the later 2007 didn’t have a 5.0 but really a 4.0. This was told to me by Dave(Stendec), they also don’t have the boost valve. You physically couldn’t get the schrauder connection in as the proximety to the frame. When you see the manual for the shock at the point about boost valve there is an asterix then lower down it says not on enduro models. looking at pictures of newer SX’s it’s not untill 2009 that the boost valve was fitted as the frame was altered. Dave (stendec) told me the he prefers the DHX 3.0 anyway as there is less to play with and go wrong. Dave has also serviced and tuned the shocks. In 2006 Marzochi painted the springs that went in the forks, unfortunately the paint comes off and blocks the rebound circuit so check this out when looking at your new bike.
The 2006 model doesn’t come with two rings up front, if you are going to pedal this beasty up hill then you will need a top swing bottom pull front mech. Spesialized thoughtfully put the cable mounts on the frame for a front mech.
As as already been mentioned the 2006 SX has slightly different top tube length and head angle to the Enduro(info from spesialized archives).
I love my SX Trail, I peddal it everywhere now it’s got two rings up front. It’s more than capeable of downhill, no probs at Cannock(apart from me the rider). It flew down the Snowdon ranger path last week.
Granted it is a little heavy but you get used to it and it gets easier as you get fitter.
Hope this helps,
Si