I'm going to add a bit here that's off subject and on subject.
1. If you are putting gear into a credenza, make darn sure your credenza is designed properly for A/V gear and isn't just a hack job piece designed to look good, but with no clue at all about electronics and proper cooling. In my experience, about 10% of gear installed inside of a solid door front credenza has had heat related failures due to lousy design.
I would make sure that you have a shelf for each piece of gear going in there, plenty of space around the gear, and air in-take and out-flow so that cool fresh air can get to the gear at all times. Also, provision for fans to possibly be necessary.
2. Clear glass is no issue for IR. IR is light, simple as that. You gotta have line of site with light beams, but you can also reflect the light off of other things. So, clear glass is good, frosted glass likely will interfere with the light to much to make it reliable.
I personally would recommend, if it is a straightforward setup, a Harmony Remote with RF capabilities. Forget the IR repeater system, but go this route and put the RF receiver inside the credenza. RF (radio) is not line of site and requires no specialty cabling. You put IR emitters on the front of the gear in the rack, and the remote takes a few hours for a novice to program and they have solid technical support to call if you get confused.