[ZTE Axon 7 Themes, Apps, and Mods] Infy_AsiX:
There's a Nougat Dolby port confirmed working on 8.1 ROMs. Thanks to [MENTION=7340768]roisuke[/MENTION] guide (and permission to repost for info) on the LOS15.1 thread summarising steps similar to the original Pixel 2XL guide, which uses the old ARISE N Dolby Atmos zip. In roisuke's post, his/her reason for trying this old Dolby is the newer Dolby boot loops on LOS15.1. In my case I was looking for a better compatible and audio quality Dolby when I found out about it. There's a few reasons i'll group into headings below. I know Dolby speakers that we paid for on stock for our device is a loved feature sought by more than just a few of us. I hope to help improve some people's speaker audio experience like I have, finally rivaling stock performance with V4A extra on top :laugh:

For installation instructions I'll just link roisuke's post, as mine has more to do with settings and usage explanation. I will just add that I had a different issue installing that Dolby zip on RR-O, the process would freeze without an error, requiring a force restart. The zip isn't detected by Magisk Manager and so can't be installed there. I couldn't install the zip when any Magisk version is installed. I ended up having to uninstall Magisk to allow the zip to install to system and then follow up with the other Magisk audio mods installed normally, Viper4Android (i'm on the old 2.3.4.0 for it's Super driver and better graphic equaliser), Ainur Sauron (optional maybe, it claims to improve audio in system and targets Axon 7 as well, I haven't tested this mod without it yet) and lastly Audio Media Library. Also thanks to [MENTION=319057]Oki[/MENTION] for pointing out the hifi DAC patch is necessary with this particular Dolby mod.

Nougat Dolby sounds better

The reasoning is that I've recently been testing custom ROM N Dolby and it sounds just as good as stock N had. While I tested Oreo Dolby ports back when the B32+B10 bootstack was new also just recently too and found it didn't sound as good as N's. Therefore I understand it's not a custom port issue that the new O Dolby sounds worse than N but that it's the updated Dolby itself.

It can work together with V4A

A benefit of this old N Dolby is it is working with current V4A whereas I can't seem to get the new O Dolby to run with V4A, it did when I tested months ago but I can't recreate that either. A benefit to using V4A in combination is it's "Firequalizer" to preset "Small Speakers" accentuates bass and lessens the tinny treble, this is something I used to do back on stock N as well.

It can be configured to set and forget

A little talked about but great feature of stock Dolby is it remembered the settings separately for plugged/unplugged and for each individual app last playing audio too. That made it so good being only on for internal speakers as I preferred and would change settings mode automatically when you stopped audio and started in another app.

Custom ROMs with Dolby ports doesn't remember states, however with a bit of compromise it can be used as such on this N Dolby if you prefer Dolby to only affect internal speakers. The trick is to set no extra filters and EQ in Dolby but just have Dolby enabled. With all other settings off, it still positively affects speaker audio but has no affect on headphone jack audio, you can test this by listening either way while switching on and off. This works combined with the V4A equaliser settings as previously explained. Set rather simply as so, the speaker output has less harsh treble and increased bass to sound similar in presentation to listening on quality headphones.

Extra notes

A shortcoming bug with this N Dolby port however is the Surround Virtualisation feature doesn't work on speakers. It seems reversed and only works when plugged in, I find it best to leave it off as preferred and it will stay off. This bug is unfortunate as the surround was always nice in my opinion, but it's only one loss compared to all the other gains. For what it's worth I couldn't audibly hear a benefit of the surround feature on the O port in my limited testing. Also consider if using the O port where the effects are all somewhat changed for worse in my opinion, it also has to be manually switched off afterwards to not affect plugged audio unlike with the workaround available in the N port. In terms of comparing missing new features, the Oreo version has a bass boost toggle and a dynamic setting, overall though I couldn't settle on an audio setup I liked with any Oreo Dolby settings.

Conclusion

I hope my experience will help others to finally get the most out of their speakers with Dolby and V4A. Since moving from stock N to custom Oreo in early April left me disappointed in O Dolby quality usage issues, I'd stopped using it and relied only on V4A's Speaker Optimisation setting for improving the speakers as a compromise but it always left me wanting in comparison. However now recently finally figuring all this out, i'll be using this for the forseeable future. I really adore the loud unbeatable quality Dolby speaker output for general listening, I mean even a dozen meters away it sounds transformed like a good dedicated mini speaker is playing. This coming from someone who appreciates listening on premium headphones too.