theyre both called OE on the end, for 'Open Embedded'
the twin has a few extra outputs on the back, like VCR scart, Component video outputs (Y Pb Pr) and an IF loop thru, it also has 2 CI+ slots (slightly different to CI)
but, the 2T has MASSIVE amounts of extra flash memory, and is a little cheaper (259 & 219)
the twin can take a 3.5 or 2.5 internal hdd, but the 2T can only take a 2.5 internal hdd
end user wise, they are identical though, they run identical images, the remotes are laid out identical (and are intechangeable with button presses on the front of the receiver)
i guess its down to internal storage Vs external connections (and a price difference of 40 quid lol) the 2T has more internal storage, the twin has more external connections and costs £40 more
they both have HDMI, TV scart, video, stereo phono, optical audio, 3x usb, rs232, twin sat inputs, ethernet and programmable RF outputs (for viewing in other rooms in the house via co-ax cable)