There are lots of wireless ear buds available, and for the most part they all work fairly well. Most cost about $200 to $400 at the online stores, but you may want to check with our friend in New England first.
Now, when I wandered through the audiences with a wireless mic and sang to the ladies to a midi file, I never needed ear buds to hear what was playing. If I would have, I would think that my sound system was not providing adequate volume levels and good dispersion in the venue. This may be your problem if your wife cannot hear the music that is playing very well in remote areas of the venue. Never had that problem since I switched to the Bose Vertical array systems. In fact, the only problem I had while singing to the ladies was them trying to grope me, which I thoroughly enjoyed, so I guess it wasn't really a problem.
Good luck,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)