One alternative would be to add tweeters that surface mount and also swivel. The high notes are very directional and that might give you a little more control.
Our coach has the cubes and I moved the right one to the driver's side of the front TV cabinet. That allows me to turn up the volume and not hurt my wife's more sensitive ears. The wires were pretty easy to find behind the front TV and cabinets. I extended the one and remounted it.
2004 37B Adventurer, 8.1 WH, Ultrapower, DIY CAI, Henderson Track Bar, Tru Center, Koni FSD's, Roadmaster Even Brake, Scan Guage II, 180 Thermostat,