>>So should i update to 2.61 first and then to 2.73?
You would be better off going for version 2.61 first yes, if you find the Wireless performance low, simply apply 2.73.
>>>> With DMT, all you do is force the router to ignore the DSLAM/MSAN target snr and sync with its own (i think, correct if I am wrong)
Depends on the router.. its basically called over-riding the one set on the DSLAM, by getting it to negotiate at a % OR at dBs lower than set.
IIRC You'll notice that some versions of DMT are different and some set at a % and some at dBs.. hence why you often have to play with the slider to find the right level.
With the DSL-2740B, you can go lower that the 10% max the slider provides by using a simple command:-
adslctl configure --snr 1
With the above, simply replace the 1 with any number 1-9 and that will bring it right down, in my case to 6dB target.