I am not Kevin, so I will have to beg your forgiveness (pleasedontsueme), but I feel like taking a poke at this. I am just guessing at North Star's reasoning for using IC opamps for the output stage on the Mk2 v. Mk1, so could certainly be wrong.
The North Star m192 mk1 used a voltage out DAC, CS4396 IIRC. Discrete output stages for v-out DACs are very easy to design, as the output requires nothing more than a buffer and LPF, and there are plenty who even feel that that is redundant, and take the output straight off the DAC. You can make a great buffer with just a pair of JFETs, or a simple discrete opamp, or whatever floats your boat. Works great.
The North Star m192 mk2 uses a current out DAC, PCM1792 IIRC. Discrete output stages for i-out dacs are much more difficult to properly design, though there are a few approaches you can take. Common base/source amplifiers are a good way to do this, though I am sure there are those who use simply a discrete opamp. Some also use a passive I/V and discrete gain stage follower, though this really isnt a good approach (IMO). It is much, much easier to just use opamps for the I/V conversion, and they work well enough for most.
With a discrete design, you get to choose everything. If you dont want to use NFB, and there are some good reasons not to here, you dont have to. Its more about choices I guess. You can also bias discrete parts much hotter than the transistors inside an IC opamp.