Here is an update on the situation as promised ..
I have installed 3 x 120 mm Arctic PC cooling fans at the rear of the AV unit. They are set up to extract hot air out of the unit, with the door being kept open about 2 centimetres to allow cool air in. The fans are powered by a Phanteks fan controller which has a 3 speed, wired remote control.
This has helped significantly, with the outside cases of the CD player and amp being cool to the touch now
.
I located the fans at the same height or slightly higher than the top unit on each shelf (which were the CDP and Amp).
As an aside, the Sky Q box which is notorious for running hot, still runs very hot (which is placed on the very top shelf with its own extracting fan too). I think Sky must source their components from Breville?!!