I thought about trying to switch to foobar2000 mobile but was a bit intimidated with having to ftp transfer tracks to my phone. Since m4a works I think I'm just going to convert the mp3 tracks...not an ideal solution but then I don't have to mess around with it anymore. Thanks for trying to help!
I transfer the files to my iphone using itunes on windows and connecting my phone, just as if I was going to use the apple music app. But once the files are on the phone, I can play them with foobar2000 mobile.
Just to follow up on the foobar2000 mobile side issue, I recalled that I had recently purchased TuneFusion (from the maker or dbpoweramp). It turns out that TuneFusion can automatically transfer songs/albums etc. to an iphone/ipad and other portable devices (including over WIFI). I played with it a bit last night. It has several interesting functions. The two best I've found for me are that (1) it can automatically convert lossless files to a lossy format upon transfer to my iphone, retaining all tag and art info, and (2) it has a "smart" sync function which will transfer only certain items based on user customization.
With this functionality, I can truly drop the use of itunes for any music related purpose.
I downloaded foobar2000 mobile again last night. I see that I can play my music thru that app but it does not add my playlists in as well. If it would grab my playlists too then using this app would be a no brainer. I know the Cesium music app can grab everything from itunes but it does not support replay/gain. I wish foobar2000 could just learn how to grab everything from itunes like the Cesium app does...it would greatly simplify things
I started experimenting again and comparing how MP3Tag writes the COMMENT ITUNNORM field as compared to iVolume for one of the troublesome MP3 files I have that is not showing the correct SoundCheck value in iTunes and here is how they were written. Note that the album replay/gain value calculated in Foobar2000 and dBPowerAmp using the EBU R128 at -18 LUFS was +2.44:
MP3Tag: 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A (imports as +2.0 dB for SoundCheck because iTunes analyzes the track)
iVolume: 0000023D 0000023D 00000599 00000599 0000BD60 0000BD60 00000000 00000000 0000D0C8 00009138 (imports as +2.4 dB for SoundCheck)
I then took this a step further and looked at the files in a hex editor to see how the COMMENT ITUNNORM field has actually been written. The only reason that MP3Tag is not working to write the values to an MP3 file is because of one tiny little thing:
MP3Tag: COMM...i...0000023A 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A 0000023A
iVolume: COMM...h...0000023D 0000023D 00000599 00000599 0000BD60 0000BD60 00000000 00000000 0000D0C8 00009138
If I change the "i" to an "h" in the hex editor, then the COMMENT ITUNNORM value that MP3Tag writes imports into iTunes correctly. I don't know what the "i" or the "h" means but hopefully someone else can take it from here and make the necessary changes so that writing these SoundCheck values works for MP3 files.