'Digital' seems to be a marketing gimmick! In the Hoya line, Hoya publishes that the light transmission thru the double coated is 93-94%, thru the HMC is 97%, thru the SHMC is 99.7% (B+W has 99.6%, newest Heliopans have 99.8% tranmission). The 'digital' Hoya have a number of newer gimmicks 'for digital'...I call them gimmicks because unlike any of their prior features, Hoya publishes NO QUANTITATIVE assessment of the benefit from any of the digital features! And they somewhat reluctantly acknowledge that the 'digital' filters only have the same transmission as the HMC filters, at 97% ! The newest line, the HD line comes closest to equalling the transmission performance of the SHMC at 99.35%, but it still falls short.
Hoya Single coated = 94% transmission, Hoya HMC = 97% transmission, Hoya Digital = 97%, Hoya HD = 99.35%
B+W MRC = 99.6% transmission, Hoya SHMC = 99.7% transmission, newest Heliopan = 99.8% transmission