See notes by Deligne/Voevodsky for a proof of the fact that the Eilenberg-MacLane spectrum represents motivic cohomology.
The etale preprint of Quick
The preprint of Jardine treating abstract representability theorems for stable model cats
Hornbostel on hermitian K-theory and Witt groups
Possibly the following fact is of interest: The contravariant functor from to Huber’s triangulated tensor category of mixed motives extend to a functor on smooth simplicial schemes over . See Levine in K-theory handbook, page 475.
Yagunov on rigidity for theories represented by T-spectra. This seems to be generalized here
nLab page on Representability in algebraic geometry