Devialet Phantom studio monitors for pro

[Pleyel]

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A lagless analogue audio source would be the deal maker

It's probably already lagless when used in mono and fed by optical, since no network transport is needed (if not lagless, it could easily).
In which case, one mono (L, L) S/PDIF into a Phantom, and one mono (R, R) into the second Phantom (each configured for mono use) should do the job ;-)