When do I need to be concerned about impedance mis-matching when dealing with XLR <-> 1/4 connectors on the same cable?

For example, do impedeance mis-matches only occur with XLR(bal.) <-> TS(unbal.) ends as opposed to XLR(bal.) <-> TRS(bal.) ends?

Please clarify and reinforce this concept for me for me, it would be MUCH appreciated.

The reason I ask is because I will begin using outboard pres sometime in the near future. I plan on taking the line level outs from the pres, sending them straight into my bal. MixWizard line level ins, therefore bypassing the preamp stage (duh). I just want to make sure that I fully understand the concept of cable connection impedance properties before I begin building the cables.

Thanx for your patience and take care,
-wes-