analog amplifier questions

[1uk3]

hi

i'm building a little device to measure LCR, phase shift, non-linearity,... + a simple signal generator
therefore i generate a signal (DDS <=1MHz, 16MHz sample rate), amplify it, and do a 4-wire voltage/current measurement
i'm not very experienced in analogue circuit design, so i'm very thankful for tips.

problem: for the signalgenerator i want to adjust the amplitude digitally, but i have no idea how to do that!
i doesn't have to be very accurate and i only need 10-20steps
maybe a digital potentiometer instead of R9?
i try to use cheap parts, so please don't recommend very expensive chips!

her is what i have so far(from left to right):
signal from DDS chip(0-620mV) --> filter --> AB-amplifier -->DUT --> shunts --> voltage/current amplifier --> ADCs
SEE ATTACHMENT!

i didn't put much thought into shunt and op-amp resistor values jet. i first want to know the output voltage range

can you give me some hints please?

many thanks
lukas


and sorry for my bad english