You can see the digital speed in the hidden test menu-

But as far as coding, there is no easy way to enable digital speed with the e53 chassis.
I don't think anyone has done it with e53, certainly can't do it just by changing a value in NCS expert.

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X5 E70 3.0d M-Sport , 2010 Titan Silver , ZF 6HP28, 320hp.

X5 E53 3.0d Sport, 2006 LeMans Blue, ZF 6HP26, diesel .