Jla, I am not familiar with the finish that Proac gives to their speakers, so I am hesitant to give a suggestion that might otherwise ruin the effect of your finish. If the speakers do not have a high gloss lacquered or a varnish-based finish, you cannot go wrong with 100% tung oil or boiled linseed oil. Most of the commercial wood care products are crap. They don't protect the wood and just kinda float on the top of the surface. They look good for a time, but quickly lose that "fresh polished" look and those with beeswax can buildup and look cloudy over time. Tung oil or linseed oil penetrate into the grain of the wood, offering decent protection.
Yew is a very hard, though rough, open grained wood. As an aside, yew is so dense that it will not float! That being said it can be highly polished without using lacquer/shellac, varnish. But, because it is open-grained, often a sealer is used followed by varnish. If this is the case, a high-quality paste wax is more appropriately in order.
My grandfather and I used to highly polish yew by rubbing it with boiled linseed oil. We applied a generous film of the oil, allowed it to settle for about 15 minutes, then sprinkle with powdered pumice (hard to find these days), and rubbed vigorously with pieces of old cotton bed sheets. We then repeated the process 3-5 times. This provides a very hard, lustrous, and rich finish for yew. This is a super excellent finish for birdseye maple, among other woods. I finished a clock I built 30 years ago in this fashion and other than normal dusting, it required no maintenance and still has a hard rich finish as though it was done yesterday. Might be appropriate if you ever need to refinish your speakers. For simple maintenance, I would suggest rubbing with tung oil maybe twice each year. There is also a product called Danish oil that is part oil and part varnish. It works well, too, but I would inquire as to the finish products used in your Proacs before using any varnish-based product. As with any wood, keep out of direct sunlight if at all possible. If not, rotate the speakers if only one is subject to sunlight.
Sorry to blather on, but I love speaking of wood. For those wondering why yew might be more expensive as a choice for speakers, consider that the yew does not grow much more than 20 feet high and about 18 inches across. The sapwood is rarely more than an inch deep and can contain NUMEROUs knots. So, those very light colored yew speakers are made from wood that comes from a relatively scarce, short, limited-girth, and limited-sapwood tree. The veneer is "peeled" off on a lathe-type machine with the log positioned horizontally. Fun to watch.
