I think I had very similar impressions of the DACport original vs the borrowed DACport LX + amp. I also think the DACport uses OPA1611 or OPA1612 opamps, if I recall correctly from what Michael told me at CanJam when the DACport was first introduced. I agree that the original DACport does seem to have a little bit more warmth and a little less micro-detail in return for a little more euphonic and less analytical sound.
As for the Stepdance - I thought the Stepdance, RSA P-51 and SR-71b were all on a similar level of performance which was outstanding for a portable, where the main differences were in power outputs. The P-51 had the least power, Stepdance noticeably more, and SR-71b slightly more than that only if used balanced. For single ended phones the Stepdance won out for combination of power and quality.
However, at the time I compared them (using Pico DAC and DACport as source) I had two stepdance prototypes with different opamps to test, and both required using my 12-15v external PSU as the battery bay wasn't working yet, buy Jan assured me that the 9v battery would give the same level of power through voltage regulators. The OPA1611 won out as being the best for everything but HD800, and still acceptable for HD800. The other prototype was slightly better with HD800 but suffered with everything else.
In the end I didn't think I needed to add a DACport LX to my gear, being quite happy with the original DACport since it came out.