the dart 108 is my favorite stereo amp. i owned it for 8 years, and at one point owned a pair of them. i owned it before and after the SCNP upgrade and that is significant in terms of controlling a speaker at higher SPL's. the 108 has a super sweet and extended top end, transparent and natural timbre and tonality, and articulate bass. very cohesive and balanced. will bring out the best in a speaker appropriately matched to it.
I'm a person with tube amp tendencies, and view the dart 108 as the best solid state amp for a tube lover. the dart's very low parts count and minimalist circuit gets out of the way of the music. you hear music, and not like listening through a bunch of circuits.
you do not list your speakers or room size. the dart 108's are reasonably flexible in speaker synergy but harder to drive speakers in larger rooms might be beyond it's safe design envelope.
the Pass Labs would be on my personal very short recommended next level of solid state amplifiers below the dart 108. the Pass Labs has a natural tonality and listen-ability.
personally i've not done head to head compares Pass Labs to the dart 108. you can look at my system page and see my current dart mono block amplifiers.....which are the only amps I prefer to the 108.
good luck with your decision.