3.5mm to RCA cable suggestions.

I would recommend these from personal hands on experience in identical circumstances . They were dealer recommended for my desktop nearfield listening "C" system

AUDIOQUEST Evergreen Interconnect 3.5MM to RCA

Personal hands-on opinion:  

-- Surprisingly good for their specific application:

--iPhone (with ONKYO HF hi-Rez player app ) source playing hi-Rez 24/96 downloads and hi-Rez 24/96 TIDAL streaming AND USB port out of my PC or MacPro to bypass the internal crap soundcard

--Audioquest DRAGONFLY (USB to 3.5mm)  mini port headphone amp/microDAC

-- the AQ Evergreen 3.5 -RCA interconnect above inserted herein 

--AQ RCA cables now plugged into the L-R RCA inputs in the active amp powered KANTO YU-5 speakers with a subwoofer RCA cable out from there to an active Subwoofer 

Highly recommended 

Thanks for the advice,

Those don't look too expensive for my modest desktop needs. I'll only need .6m anyway. It sounds like you have a nice setup. I'm rolling with Mackie MR8s and soon an AudioQuest Beetle DAC/BT adapter (when it's released). I might add a small tube preamp after the DAC and before the speakers. Right now I'm running straight out of my MacBook Air. I'm not ready to drop the cash on some KEF LS50 Wireless speakers yet so I'm trying to get the most out of what I have.

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

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