I am using the KRK solely for music listening.
I wonder what effect will add if I buy a Little Dot mk_iii as preamp in between DAC and KRK?
There's no telling how much difference the tubes will have with the Rokit and whether you'll actually like it. However, I think there are passive preamps around that can be had for around $100USD (can't remember the brand, sorry), so given they won't color the sound too much you could use this just to put a master volume control within reach.
Or if you need a headphone driver too, you can just replace your DAC_I with the DAC_II, or other DAC that has a preamp (and a headphone amp if you need that).
Hard to tell exactly how, but since you don't mind coloring it, it's a viable option. However, there are those passive preamps if you really want to just be safe about it.
Are the monitors you are using powered or are they passive? I have emotiva 5s and am using a peachtree decco 2 as a preamp. It seems to work pretty well for me as a preamp for my active monitors.The peachtree integrated amps are very flexible and can work pretty well as a preamp/dac if you do not need the onboard amplification.
I have not heard my decco 2 amplifier section so i can not comment on the amplifier sections sound but if your monitors are not powered it could work ok as a integrated and would greatly simplify things, beeing all things to all people.I bought my decco 2 from peachtree directly.I got a refurbished unit and saved some money.The unit carries a same as new warranty and I have had no issues with its opereration as a preamp/dac in my set up.
You might want to check out the peachtree products. good luck in your search for a preamp for your monitors.
I forgot that the peachtree integrateds have a defeatable tube buffer stage in their designs (again flexibilty of selection) which is another feature available on their comprehensive products.
This may just what you are looking for and it wold also greatly simplify your set up.The dac section is pretty good too but the decco models only will do 96 khz.The I inova model will do 192 but it is a fair amount costlier than the decco models.