Alan,
The oak arm-board looks great, and I'm not surprised you are getting an even better sound as oak is an excellent choice of material to use for minimising the transfer of vibration(s). Russ Andrews uses oak for his equipment support feet, I have used it for my isolation platform (supporting the Gyrodec) with excellent results.
I must admit when I saw your original photo with just the plain acrylic arm-board, I thought it looked a little dull, fitting the oak top massively improves the aesthetics.
A suggestion you may want to consider is given the excellent material properties of oak, why don't you or Peter, make the entire arm-board from oak, it would be cheaper than acrylic/Perspex, and IMHO look much better - just a thought.