Congratulations on acquiring a really nice cartridge. The O needs a good 50-70 hours to begin revealing itself and mine took upward to 120 hours until I thought it well run-in.
I don't use a step-up transformer, so I'm no help there. On several different phono stages I've found 100 - 200 Ohms is a good place to start for resistance. I've finally settled on 170.
Having the stylus azimuth set properly pays big dividends with the Orpheus. If your tonearm allows this adjustment, you can set azimuth with a meter and a test record, or by ear. (Several good threads w/ azimuth discussion.)
Tim