[rockdoe]

although Opus is very nice, it's not as efficient ... as HE-AAC

Uh, no, this is not correct. If you try to find a source, you'll easily find the opposite is very well established.

[CharlesW]

Here's a "Quality vs Bitrate" chart from opus-codec.org, the home of Opus: https://opus-codec.org/static/comparison/quality.svg

Note how AAC has effectively the same efficiency as Opus? HE-AAC and HE-AACv2 are notably better in comparison, and are usable at lower bitrates than AAC.

In cases where "the opposite is very well established", they're talking about AAC-LC. Citations that show otherwise are welcome! In any case, HE-AAC's universality is really beaten only by MP3 (which it trounces).

[ksec]

I assuming you are using HE-AAC at below 96kbps? Because above AAC-LC should perform better.