The Trimble S8 datasheet lists the direct reflect maximum distance at 1300 meters and 800 meters for a material like concrete:
http://trl.trimble.com/docushare/dsweb/Get/Document-390412/022543-410H_TrimbleS8_DS_0115_LR_sec.pdf
Anyone tested this to see what the actual capability is in the real world?
If it isn't dr+ I highly doubt it
DR+ is fine with me, our horizontal accuracy requirements are quite low.
If you are trying to measure at that range then the size of the beam is going to be huge so you are less likely to read smaller objects reliably.
I have measured at 1100m in DR mode (S6 DR Plus) but it was a railway mile post and I think it may have been at least slightly retro reflective.
The DR mode is set by default to measure 1 to 600m. You woukd have to change this in the EDM settings screen. Switching to tracking (or coarse mode) will also help.
As Ralph says there are various evolutions and options on the DR hardware. The other options apart from DR Plus (DR, DR200, DR300+, DR HP) are not going to be up to it. You can tell whuch you have by the label under the eyepiece.
I have a 0.5" S8 with fine lock which does not have DR+ and I'm lucky to get 100mts and it better be a retro surface. That particular instrument was not designed for that intention. So like squowse said, check and see which version of DR you have or if your instrument has it at all.