The absolute "best" filter/conditioner for digital

Have you tried combinations of approaches?
Zd542 is right on the money. The Cable Co. may not carry everything (who does?), but they carry Pure Power+, Silver Circle Audio, Shunyata, Audio Magic, Running Springs, Audience and Furutech. The heavy hitters, in other words.
Two relatively iconoclastic audio personalities have approached the conditioner question and produced modestly priced products that reliably reduced interference, and subjectively cleaned up, shined up, and polished the sound reproduction in my systems.

Mapleshade's power strips - the stealth power conditioners masquerading as humble power strips. These outdid the benefits of a number of other more expensive "real" conditioners.

Machina Dynamica's provocatively and humorously titled "Flying Saucers" for windows which are tiny, home-made looking trimmed pieces of treated copper which even more dramatically improved the sound reproduction of every audio and video device - even down to the level of tabletop CD boombox!
Important note: At no time was any hallucinatory mushroom ingested.

I venture to guess these are among the most cost effective items to try.