Easy gents, after all, it's just a hobby, right?
Coincidentally, I just recently acquired an Ayre QB-9 from one who sold it due to its incompatibility with the Squeezebox, which his wife loves.
Here are the issues - The QB-9 not only requires a USB connection, but also the installation of Wavelength Audio-designed software on the PC or Mac used as a source. This supports the handshake between source and DAC to manage asynchonous mode transmission, and virtually eliminate significant jitter.
So Rocca, you can see that KGTurner, et. al. have it exactly right. You might check some other Agon threads for recs on good transport-sourced +external DAC combos. Be aware, though, that recent computer-based source/DAC technology has IMO caught up with (some say surpassed) the benefit/cost of Transport + external DAC.
But as you know, the Rega Planet is a very good CD player and it will be difficult, IMO to find an external DAC that will improve sound while managing jitter, clock synch, and power supply, near its price point.
Marcober, despite the above-mentioned problems with the implementation of QB-9's supporting software thru the Squeezebox, there ARE some enterprising dudes over on the Squeezebox Support Forum who are right now trying to solve this very problem!
I don't know Squeezebox myself, but it seems that it's emminently versatile and programmable for controling its hardware interfaces. If you happen to find a solution over there, please post back to us!