The mini xlr's sound fine to me, if you go with the rean ones they are brass with gold plating which is about the same as any other connector. The switchcraft mini xlr has arguably a slightly worse locking mechanism (I don't really think it matters), but if it is important to you they can come with silver pins. To get better connector material you would have to be spending quite a lot for fancy full sized xlrs so I wouldn't worry about it too much. Almost no matter what you are going through some silver or brass & gold or nickel contacts coming out of your amp, and I doubt if the length of silver or brass introduced in a mini xlr connction is going to make a big difference in audible quality when your cable already has something similar on at least 1 end, both if they are detachable cables. The only time I would say you really need to avoid them is if you are dying to use 20awg or thicker wire.
Consider this, the lcd2 requires 1 4 pin mini xlr for each ear connection, they can't possibly screw up the sound that bad if they do at all ;p.
In my experience this is the case anyhow, YMMV.
Also, there isn't even a boutique full sized 4pin xlr in existence that I know of, so for better connector material you're generally talking dual full sized 3 pin xlrs for a balanced connection. The pins themselves are roughly 22awg I think.