1) I *DID* install the subtitle external font as a sysem font; if you'd read my OP you would have read that as well. ConvertX DID NOT use that font.
2) The link you posted states that karaoke effects were not supported - they partially are, however - which was unexpected but welcome.
3) That still does not explain the huge font substitution. In my defaults I had Arial 20 - the font used in the English subtitle is anything BUT Arial 20.
4) The font used in the English subtitle is not antialiased; therefore showing extreme cases of the jaggies.
Thanks for posting the link (though I already had - it was in response to a suggestion I had put there) - what I was asking (as was said in the OP) was "How can I get this to at least resemble the original .MKV picture, as in at least rendering a usable subtitle at something approaching the proper size, antialiased to remove jaggies"?
If you're trying to tell me that ConvertX can't do at least that, then they should remove support for SSA and ASS format subtitles permanently, and state that in the product description.
An I a little frustrated? Yes. I REALLY don't want to have to import each file into something like Premiere and have it do a hardcode - I'd like to keep my multilingual options intact. Not to mention how much time the double encode would tanke - AND the losses involved (original files are 720p resolution h.264/AAC)