Is it possible to transcode mp3 to Ogg with no additional quality loss?
If it isn't, how to transcode with the least possible quality loss (with remaining at approximately the same bitrate)?

Thanks

Nope, anything you do will result in a reduction of audio quality.....but depending on your gear, your ears or your music it might still be listenable. I would just leave the existing file the way it is but if you must transcode a piece of freeware called dbpoweramp music converter will do the job.

Off the top of my head there is ogg support natively...or maybe it requires a plugin, but in any event a Google search and a visit to their site will get you where you want to go.

I have no vested interest in the company or its product...just have used it once or twice for transcoding to satisfy my own curiosity.

rs

Using dbpoweramp for a few years now...
which is better, the ogg-plugin, or should I create a generic CLI from oggenc2 (aoTuV)?

The default dMC Vorbis plugin appears to be based on the official 1.1 release. If you wish to use a specific version of Vorbis, set up a CLI. (you probably knew this )

But the question remains as to why you would want to do this... I tried it once a while back on a large set of songs in the -q4, -q5 range and, while some of them were not percetible, I received horrible results with a few files.

Try vorbis 1.1 with quality about 25-30% lower than nominal in kbps with options: --advanced-encode-option impulse_trigger_profile=6 --advanced-encode-option impulse_noisetune=-10 --advanced-encode-option lowpass_frequency=18,5.
Though I won't guarantee that bitrate won't fluctuate badly, but at least this will be pretty imperceptible to you I think.
And don't forget renaming it to *.mp3.ogg if you ever share it.

I'll try that... Are there any other --aeo switches that I might experiment with in general? Is there a list of those somewhere?
Thanks.