--alt preset cbr 192

AND

-b 192

Well, are these two the same in terms of audio quality?

FYI, I'm using HA's recommended 3.90.2 compile(from the sticky).

Use --alt preset cbr 192. This uses nspystune whereas plain -b 192 uses gpsycho. nspytune is the preferred psymodel for LAME.

And there's much more to it than that, too. Specialized joint-stereo and other code-level tweaks in --alt-preset cbr 192.

how about --alt preset vbr 192

No such thing.

There is, however, --alt-preset 192. What this does is encodes using ABR (average bitrate - a special VBR method) around 192kbps. But as long as you're not encoding complex techno or metal music, I would use --alt-preset standard to get VBR around 192kbps. (For metal or techno, Standard often averages out at around 224kbps.)