SE--single ended, made with a braided shield coax cable.
DI--differential input, made with identical wires braided together. (the guy said this was more higher end amps. No mention of tube or ss.)
Is the single ended they refer to as an amp input type, the same as the SE stereomour I have? Or is that term used for other types of technologies or other types of parts, etc.?
This is a topic that comes up a lot on audio forums, with a lot of misinformation floating around that really confuses things.
There are balanced (xlr) and unbalanced (RCA) cable interfaces. The purpose of balanced cable interfaces is for noise reduction on long runs of cables. This is accomplished by having the impedance from signal hot to ground equal to the impedance from signal cold to ground (hence balanced impedance). There are
tons of high end audio manufacturers who will make a lot of claims beyond all of this, which you have to evaluate cautiously.
Within a given amplifier or preamplifier, you could have a differential input stage, push-pull input stage, single ended input stage, etc. There isn't a strong correlation between any of these typologies and equipment prices.
For the purposes of making cables to use with the Stereomour, you can certainly use braided wire, coax, shielded twisted pair, twisted pair, etc, provided you have RCA plugs on both ends.