Yes, OGG is losely, but I don't think that's an issue. I've never seen anyone editing sound files, and its far better to remake something from scratch then. For most sound effects, such as explosions, strange beeps and whistles of spells, and voices are perfectly fine at 56kbps, though music should be 96 or 128 kbps.
Might I ask how you converted (what program) for the mass conversions? Did you also change the XMLs to link to OGG instead of WAV files?