... or use the volume spinner for that particular part. The 'Global Volume Adjust' in RealTrack Preferences may help but increases all RT volumes.

If neither of those is adequate, you can edit the style and adjust the volume of a part. Use the StyleMaker, press Misc then press More. There is a section to 'Assign Soloist or RealTracks to style'. Select the instrument (part) to edit and increase db Offset to increase the volume. OK back to the StyleMaker and Save the style. As a precaution, you should have a backup copy of the style before editing.