Analog vs Digital attenuation for an ADC
In situations like this it's best to view the quantisers (ADC, DAC) as a noise source, and your task is to maximise the total signal to noise ratio (SNR).

FYI, an ADC/DAC has a max SNR of 6.02*b+1.76 (where b is the number of bits or ENOB).

So your best option would be to maximise the signal at the worst quantiser. So if you have an 8bit ADC and a 10bit DAC then max the ADC input signal and reduce the signal (and noise) by reducing the signal digitally but keeping the extra LSBs introduced by the gain reduction.

If you have the freedom to choose your ADC and DAC, I'd max the ADC signal and choose a higher resolution DAC to accommodate the extra bits generated by the gain reduction.

As a rule, the change in SNR as the signal changes in amplitude is fairly linear. A small additional reduction (1 to 2dB) can occur for large signals (say 1/2 scale) due to DNL and INL. So this should not be very relevant for you to consider.