3.5mm to RCA cable suggestions.

Regarding proper grounding, I would expect that a stereo 3.5 mm to dual XLR adapter cable, such as the Hosa cable the OP linked to earlier, would accomplish that. Presumably it connects the ground of the 3.5 mm plug (the "S" of its TRS connections) to pins 1 and 3 of both XLR connectors. Pin 1 is the ground connection of an XLR input, and pin 3 is the signal pin that should be grounded when an XLR input is provided with an unbalanced signal.

The cable presumably also connects the "T" (tip) of the 3.5 mm plug, which conducts the left channel signal, to pin 2 of the XLR connector that would be connected to the left channel speaker. And it presumably connects the "R" (ring) of the 3.5 mm plug, which conducts the right channel signal, to pin 2 of the XLR connector that would be connected to the right channel speaker.

That would all function in a reasonable manner. However, for the reasons I stated earlier connecting via RCA would most likely be preferable.

Regards,
-- Al

Here is the 3.5mm/TRS also:
http://www.musiciansfriend.com/accessories/kirlin-original-y-cable-3.5mm-trs-plug--2-x-1-4-in.-mono-...

The same comments I had about XLR vs. RCA apply to the Kirlin 3.5 mm to dual TS (not TRS) cable linked to above, vs. RCA. Also, I’ve never liked 1/4 inch connectors because in my experience the contact they make can sometimes become intermittent, especially if they happen to be jiggled.

Regards,
-- Al

Excellent point on the TS jacks AL.

Just a side question...is there any advantage to upgrading power cords on powered monitors at this level? I was thinking something like Pangea AC 14SE MKII.

Thanks again for taking the time to offer your experienced help.

You're welcome, Asahitoro.  Regarding whether or not a power cord upgrade may benefit this particular speaker, though, I have no idea.  In addition to depending on the design of the speaker's two internal class AB amplifiers, and on the characteristics of its stock power cord, it could conceivably also depend on what the AC line voltage happens to be at your particular location.

Good luck.  Regards,
-- Al