After my disappointment with the Modi>Vali>HD650, I've been auditioning the Gungnir>Vali>HD650, and I'm shocked at the difference in sound. With the Modi chain, the HD650 sounded flabby and hazy with compressed dynamics. The Gungnir chain largely cleans up those problems and makes the HD650 sound very rich with exciting dynamics. I have to listen to the Gungnir>Mjolnir>HD650 again, but I'm not sure I've ever heard the HD650 treble with this much sparkle and clarity. The mid-bass punch of the HD650 hits like a prize fighter--maybe a bit too much, but very fun. The soundstage is intimate, but instrument separation and detail are very nice. This is one of the best chains I've ever heard for the HD650. I think some of the preferences for the HD600 comes from plugging it into muddy signal chains. The Gungnir>Vali>HD650 may make you forget about the HD600.
Schiit should never have used the Modi-sized chassis for the Vali, because the Modi doesn't begin to take advantage of the Vali's potential. The Vali deserves a high quality DAC.
Well come on, let's be realistic. The Modi costs $99 and the Gungnir costs $749.