Tried changing DoM so it makes

<meta:MainSoundConfiguration>51/L,R,C,LFE,Ls,Rs,-,-,-,-,-,-,-,FSKSync,-,-</meta:MainSoundConfiguration>

instead of

<meta:MainSoundConfiguration>51/L,R,C,LFE,Ls,Rs,-,-,-,-,-,-,-,-,-,-</meta:MainSoundConfiguration>

but "exactly the same error": https://dcpomatic.com/forum/viewtopic.php?p=14640#p14640

DOM: 67b997fb833c6e470852615c767fa2f9d333df2a on atmos branch

Maybe it's because the DoM MXF includes AudioChannelLabelSubDescriptors (the EasyDCP MXF does not) but the DoM MXF does not have an AudioChannelLabelSubDescriptor for the sync track (intentionally...)

OP switched to Bv2.0

'Application Profile' metadata extension missing for CPL
MCA Sub Descriptors missing for CPL 
Sound Track Files shall signal Wild Track Format (SMPTE 429-2 Channel Configuration 4)

https://dcpomatic.com/forum/viewtopic.php?p=14661#p14661

DOM: 148a31352765a030cd3dd64dcf4e9998b649f338
MCA subdescriptors forced off in sound asset, main sound configuration starts with WTF/
148a31-report.html
No MCA subdescriptors in the CPL because I forgot that they are read from the sound asset.

'Application Profile' metadata extension missing for CPL ...
MCA Sub Descriptors missing for CPL ...
Sound Track Files shall signal Wild Track Format (SMPTE 429-2 Channel Configuration 4 (RDD-52 Package Specification no set).

DOM: 0f6edbc8753a8f75ea503f76843651d9edd3c4a3
libdcp: 75e86accf241dc6e2d2c2235e21093a05b01b335

Same errors again.

cpl is at: 0f6edb-cpl.xml

Asked to run same again but in SMPTE Bv2.1

MCA Sub Descriptors shall be present in CPL metadata: SoundfieldGroupLabelSubDescriptors don't match between CPL and MXF, AudioChannelLabelSubDescriptor don't match between CPL and MXF
Checking channel layout of MXF - Multi Channel Audio Labeling/Layout not conform to RDD-52.
For each reel: MCA Framework Labelling is required.

So turning off MCA subdescriptors in the audio MXF doesn't seem to go well.

From examples sent by OP and Carsten, it seems we have:

EasyDCP:

• MainSoundConfiguration: WTF/L,R,C,Lfe,LsLss,RsRss
• No MCA subdescriptors in CPL nor MXF.
• No application profile

Others:

• MainSoundConfiguration: 51/L,R,C... with FSKSync (or 71/)
• Same MCA subdescriptors in MXF as CPL.
• Maybe Bv2.1 profile

How EasyDCP would pass its own DCPs is a mystery left for the reader to solve.