ZMF headphones - Cayin Tube Headphone Amp comparison - HA 3A, 6A 300B MK II - collect them all?

This video is informational and should be viewed as such via the bias of ZMF selling Cayin products. 0:00 - 0:59: Intro 0:59 - 3:09: General Features among all three amps 3:09 - 4:12: OTL VS OTC Amps, transformers, are they better? 4:12 - 6:28: Tube Swapping Considerations; price, type etc 6:28 - 7:59: Functionality Differences, the HA - 6A is kinda special! 7:59 - 10:18: Choosing between the amps - Noise, Power and Timbre + More features 10:18 - 13:59: Sound Quality Characteristics, defining the amps and more tube talk 13:59 - END: Wrapping Up, conclusions.