Looks like your Charles on the civil registration index:-
Charles M'Grath Marriage Belfast 1881 Q4 Vol 1 pg 513
Ordering the civil certificate will give Daniel's occupation, but not a lot more you don't have from the Church transcripts. Have you had a look at the actual Church records to see if the transcriptions have missed anything or if the baptisms of the children give clues, e.g. who the godparents are? St Patrick's RC Church, Donegall St, Belfast records from 1798 have been microfilmed by PRONI - if you can't get to Belfast you could try the LDS.
Modified - I have just noticed the PRONI microfilm only goes up to 1880 so no use to you - not sure if LDS would have different dates
