3.5mm to RCA cable suggestions.

Well I’m going to stick with unbalanced. If I end up going straight from the DAC to the speakers, the 3.5mm to RCA cable will be fine (I can USB or BT into the DAC). I don’t think I’d see a benefit with balanced on one end there. If I add a small tube preamp in the mix, I’ll just go with 3.5mm/RCA from the DAC to it and then RCA to the speakers.

Edit:
I just realized if I go with those AudioQuest Evergreen 3.5mm/RCA cables it won’t work straight from my DAC to the speakers. I need the cable to split into two runs of about 3ft to reach each speaker’s input. I just gently pulled apart the insolation on my cheapo cord I’m using now and it worked.

I have the options of balanced, unbalanced and 1/4" TRS on my monitors. Which is the best route to go?

As can be seen in the block diagram on page 13 of the MR8 manual its XLR and TRS inputs have an additional active stage in the signal path (probably an op amp) which the RCA input doesn't have.  Given also that you will be supplying the MR8 with an unbalanced signal it would therefore most likely be best to use the RCA input.

I might add a small tube preamp after the DAC and before the speakers.

Keep in mind that like a lot of pro-oriented solid state equipment the amplifiers in the MR8 have relatively low input impedance, which many tube preamps will not be able to drive without significant deep bass rolloff, and/or undesirable phase shifts at deep bass frequencies.  In this case the input impedance is specified as 10K unbalanced and 20K balanced.  The balanced input impedance most likely reflects the sum of the input impedances of the two balanced signal lines, so if you were to supply the balanced input with a single-ended signal the preamp would see the same 10K load as if it were driving the RCA input.

To assure that won't be a problem you would want to choose a preamp having an output impedance of no more than 1K **at 20 Hz**.  Output impedances are often specified at a mid-range frequency, such as 1 kHz, and in the case of many tube preamps (and some solid state preamps) the impedance at 20 Hz is MUCH higher than at mid-range frequencies.  If Stereophile has reviewed the preamp the measurements section of the review will usually indicate the 20 Hz output impedance.

Regards,
-- Al
  

Al, thank you so much for the very helpful info. I had to read it a few times to understand it as my electrical expertise isn’t that polished. I was considering a headphone type tube preamp like this:
https://www.amazon.com/gp/product/B00A2QMAI2/ref=ox_sc_sfl_title_1?ie=UTF8&psc=1&smid=A1V014...

Here’s a good review of it:
http://www.head-fi.org/t/284835/review-of-the-little-dot-mkii-tube-headphone-amp-pre-amp

Connected to this which would be connected to my MacBook Air via USB (or BT from other devices at times):
https://www.crutchfield.com/p_703BEETLE/AudioQuest-Beetle.html?tp=59309&awcp=1t1&awcr=105211...

So it would be: MacBook Air to DAC via USB, DAC to preamp input via 3.5mm/RCA, preamp output to speakers input via RCA.

I thought maybe it would be fun to experiment and tinker with as I’ve never had any tube equipment. Again, I don’t want to dump a lot of money into this or I’ll just go buy a pair of LS50 Wireless speakers. I made a bunch of assumptions that it would work. I used to have a pair of M-Audio BX8s that I used a 3.5mm to TRS cable with and I had TRS->balanced plug adapters on it as well. It sounded excellent but I’m sure I wasn’t taking advantage of any balanced cable benefits.

Thanks again for your experienced advice.

The specs on page 7 of this manual for the Little Dot MkII indicate an impedance for its RCA outputs of 600 ohms, with no indication of the frequency on which that is based. Most likely it is based on a mid-range frequency such as 1 kHz, and I wouldn’t be surprised if the impedance at deep bass frequencies rose to amounts that are much higher than 600 ohms, and that are too high to be optimal in conjunction with a 10K load. Although the MR8 can’t reproduce much of the bottom octave (20 Hz to 40 Hz) anyway, so the impedance issue might not be noticeable even if present. If it were me, though, I wouldn’t purchase the Little Dot unless it could be returned without a restocking fee or other penalty.

Good luck, however you decide to proceed. Regards,
-- Al

" I am probably mistaken, but I though there was a problem going from unbalanced to balanced without proper grounding."

You have it right. That's why you can't run a component balanced and SE at the same time. That's why most fully balanced components have either a switch, or jumpers you insert in the xlr jacks directly to run in SE mode.