With some amazing help from Hobo, I was able to come up with a solution!
The main problem was with trying to query by 'ID'. No matter what we tried, it just never worked well. (It could be the way that the Advanced Custom Fields stored the ID field contents.)
What did work:
- Created a custom field for the post page in which to put the Band (custom post type) post name/slug into. (Custom field was named
post-band-name
and created with the Advanced Custom Fields plugin.) - Placed the query code in the Post Template. (See code below)
- Done.