Unbalanced audio is a voltage signal referenced to ground. A typical 3.5mm TRS jack has left audio signal on the tip, right audio signal on the ring, and the reference ("ground") on the sleeve.
The power supply on your active speakers has that class Y interference-suppression capacitor between the ground and the AC. It only leaks about 1mA and isn't dangerous, but you do feel a tingle if that passes through your body (to true earth ground).
Connecting to the speakers via say a cable with 3.5mm TRS male jack on the Mac end, and to two RCA male jacks on the powered speaker end, will connect the ground on the active speakers to the ground on your laptop, which allows the tiny leakage current (allowed by that class Y capacitor) to pass through the active speakers' ground to your Mac's audio ground to Mac chassis to your body and to true Earth ground, causing the tingle. It is
leakage, not a "real" ground loop, if that distinction matters any.
Typical audio mixers have continuity on the unbalanced audio connector "grounds", so won't change anything for HobGoblyn here.
Balanced audio uses a pair of connections, a
differential pair, for each audio channel. The differential pair does not need a ground connection per se.
Your Eris 3.5 active speakers have both unbalanced and balanced inputs. The balanced inputs are the larger, 1/4" TRS ("stereo") connectors, with tip and ring being the differential pair, and the sleeve the optional ground. Note, however, that this ground is almost certainly connected to its power supply ground, and thus will convey the "tingle" if connected to the ground on your Mac.
Typical passive DI boxes (passive as in not requiring any power) are basically just an audio transformer to galvanically isolate balanced audio lines. Essentially, across each transformer, one audio channel is coupled over using a varying magnetic field. The properties of the transformer define what kind of frequency response you get at a given input and output impedances, so there are a huge variety of such audio transformers, with the "undetectable effect on the audio signal within extended human hearing range" costing several hundred USD apiece. The ones I'd use are about USD 6 apiece.
Conversion from unbalanced to balanced is trivial with such an audio transformer: on the unbalanced side, the "ground" and the signal is connected to one coil; on the balanced side, the coil is connected to the differential pair.
Many balanced audio cables have three conductors, often with the third being a shield around the differential pair. DI boxes that can break that connection between inputs and outputs usually call this breaking "Earth lift".
In HobGoblyn's case, the need is to break the ground connection from the active speakers to the Mac, to stop the tingle, while allowing the audio signal to pass with high fidelity.
I personally would do this DIY, using components that cost less than USD $30 off Mouser (and enclosure from a local Hammond importer,
Uraltone, here in Finland). The enclosure would be placed close to the active speaker, perhaps on/in the speaker stand, or on the floor nearby. The connection from the enclosure to the active Eris speaker would use a pair of shielded audio cables (often called "microphone cable"), most likely
Adam Hall 5-star microphone cable or something like Belden 8451010100 (from
Mouser) – a pair of conductors, and a separate shield – with two 1/4" TRS ("stereo") jacks at end, both connected to the active Eris 3.5 speaker. Their ground (sleeve) would be connected to the aluminium box, so that might give a tingle if touched. From the enclosure to your Mac or any other sound source with a 3.5mm TRS audio connector, I'd do a custom 3-conductor shielded cable, maybe Tasker C115 or Belden 22-24AWG 3-conductor shielded cable (like
this, link to my local store), where the shield is connected to the enclosure, but not to anything on the 3.5mm TRS male connector. This way, the audio signals should be pretty well shielded from typical electromagnetic noise that could otherwise couple to the audio signal, and cause annoying hum or buzzing, while breaking any direct electrical connection that could conduct the tiny leakage current that causes that tingling.
The commercial option is to get two mono or one stereo DI box with "ground lift", and suitable cables. It/they will do the same thing, allowing the signal to pass without direct electrical connection across that box. While the problem here is
not a ground
loop per se, it is similar: both problems are fixed by breaking the direct electrical connection between the audio source (Mac) with a 3.5mm TRS audio output, and the active speakers.
Because I'm poor and not interested in high-end audio stuff, I cannot help with links to suitable DI boxes or similar off-the-shelf products, but they definitely do exist.