Premiere opens the AAF as audio tracks
Import the AAF and Premiere places the audio: each Final Cut role and subrole on its own track, every clip where it fell, with the clip gain, automation and fades the edit carried.
The default output is standard AAF. One optional setting, the Audio Channel Combiner, groups a clip's channels into a stereo track and is not part of the AAF standard — it is off unless you ask for it, so what you deliver opens the same way in every application that reads AAF.
What it carries, and what it does not
It carries the audio edit. It does not carry the picture — fcp2aaf writes an audio AAF, and there is no video track in it. If you want the video edit in Premiere as well, import the FCPXML into Premiere for that; the two imports are separate and do different jobs.
Why send audio through AAF at all
Because the FCPXML route does not rebuild the sound the way the edit had it — the roles, the overlapping clips spilled onto their own tracks, the split edits, the conformed handles. The AAF does. fcp2aaf cuts the audio from your originals with the handles you set, so there is room to work at every cut.
fcp2aaf does not pass audio through. It reads the paths Final Cut wrote into the FCPXML, opens your original recordings, and cuts from them exactly the regions the edit uses, with as much or as little handle around each clip as you ask for. WAV, BWF, RF64, AIFF, CAF, FLAC, MP3, MP4, MOV and MXF are read straight from the drive, at any size.
Set it up once, hand it over
You choose the handles, the sample rate, the bit depth and which tracks travel, with the session drawn in front of you and any clip playable. A self-contained AAF is one file to send; a referenced delivery is a folder with the audio beside it.