Update 2! I've been listening to the Tubadour IV SE since it arrived yesterday and I'm nothing less than astounded by this DAC. I mean like I never knew it was possible to enjoy digital about as much as analog. Words I never thought I'd say, truly. Going from the Pontus II to the Tubadour is a completely different universe. SO much dimension and warm analog tone!
Now I wonder what updating it to V or even VI would bring? The IV SE has a very FULL sound. I do love it but yeah, if there was a touch more air in there and definition without sacrificing the beauty of the current tone that would be something I'm not sure I could imagine. I did inquire with Vlad on this topic before receiving my IV SE and he said: "Tubadour V is better than IV in resolution, air, soundstage. VI is the best of all Tubadour DACs. It has much better resolution, refinement, no one tone bass, big soundstage, easy flowing liquid sound."
Needless to say with that description it's likely I'll go in on the VI upgrade. Thanks for all the input folks, I'm over the moon with my DAC now 
