What you describe is not an idiom as such, although it does make use of an idiom.
"to pit (something) against (something)" means to place the two things in opposition or competition against each other. This usage is a standard idiom.
"to pit (something) against (something) technically" is not an idiom. It's just extending the meaning into a technical area. The meaning is to place the two things in opposition or competition against each other on a technical basis.
Also, note that you have placed "technically" in the wrong place in your question. In English we don't put the adverb like "technically" in between the main verb "pit" and the direct object "something". You need to put the adverb before or after the verb and objects. That is, "to pit sth. against sth. technically", or potentially "to technically pit sth. against sth".
EDIT: In a comment below, the questioner gives another example:
the champions league final will pit technically accomplished X at home against Y
This is just the standard idiom "to pit (something) against (something)", although I think you may be analyzing it incorrectly. In this case we should analyze it as:
(the champions league final) will pit (technically accomplished X) (at home) against (Y)
(subject) will pit (something) (place-adverb) against (something)
...where the first "something" is "technically accomplished X", or an X that has shown technical accomplishments, and the second "something" is "Y".