I've owned the Theta Miles (superior balanced version) and I currently own the Quad 99CDP. I prefer the sonics of the Quad 99 CDP over the Theta. The Quad is also a current version, so you can buy one new or with low hours. Also, the Quad had 6 digital inputs so you can take advantage of its excellent 24bit/192Khz DAC. The Theta has a 20bit/48Khz DAC.
The Quad does not have that Theta "overbuilt" look, but it is a great value in a CD player. The TAS review is right on. Lastly, the Quad has a truely excellent built-in volume control and an independant non-variable output. This is a great feature allowing you to connect direct to your amp if you choose to have a single source or all digital sourced system.
Enjoy,
TIC