I recently sent my OR5 to Steve for the OTL mod and it does not disappoint. The improvements are easily as significant as adding the Dynamo power supply. Depth, layering, separation, (insert buzzword here), all took a step forward. I most appreciate the tonal realism. Brass instruments are now extremely realistic. Also, micro dynamics exhibit finer gradation which is particularly noticeable on piano.
My Aqua La Scala Optologic sounds so fantastic fed by the OR5 OTL that I haven't even been tempted to try the Aqua's onboard USB. You don't need an expensive DAC to hear the differences, though. I also own an uber-modded Eastern Electric DSD Supreme and the OTL mod is plainly audible there, too.
If you are on the fence about whether the OTL mod is worth it, I can assure that it is.