Your topic heading and topic content don't seem to be asking the same question.
"Can a mini jack break down?" - yes.
"Can a mini jack to RCA cable send digital 5.1 sound?" - I am not aware of any motherboard which sends 5.1 output on a mini-jack. Some have S/PDIF output on optical (TOSlink) or coax (RCA) connections. S/PDIF can carry 5.1 sound as Dolby Digital or dts.
As far as I know, mini-jack outputs on motherboards only carry stereo signals.
BTW: It's not a good idea to include your email address in a post - you are inviting spammers to send you junk mail.
you cant have an analogue to digital , or a digital to analogue, unless the device it self is powered and as a processor, so wires cant change formats.
you cant send 5.1 DIGITAL signals, with a mini jack, but you can output 5.1 analogue,
compulsiveBuilder: al mobos can do at least 5.1 as the standard. since when could minijacks only send out stereo signals.... it could do 5.1 since 1998, and some older mobos b4 1998 could do 5.1 as well.