Tube DAC with i2s input?

@lanx0003 I very much appreciate your POV and thanks for chiming in! There certainly is a lot of validity to trying to calm down the "audiophilia nervosa" and yes, I'm deep in the throes of it currently with my DAC quest. I'm a fan of Tarun btw and I often did wonder to what level adding the DDC to the Pontus II takes it to so thanks for pointing that out.

Normally I'd take my setup as better than just "good enough", but not too long ago I was window shopping on USAudiomart and came across an unbeatable deal - a practically new Grado Aeon3 cartridge (my dream cartridge) for an absurdly low price - All checked out and I took the plunge. At the time I was running a DV XX2 MkII, a well-regarded cartridge I was more than happy with. Well, once I slotted in the Grado I was nothing less than completely astonished by the difference in fidelity. I mean a true case of really getting what you pay for with minimal "diminished return".

I see a DAC as the cartridge in the digital arena and while I really can't complain about the sound I'm currently getting, I think going to something like a Tubadour V will equate the experience I had going to the Grado. To be sure I put back my XX2 cartridge tonight and spent a fair amount of time listening to it, then went to the Grado. Yup, just as floored at the difference as I was initially.

So while I have a perfectly fine setup now, I'm going to wait until the right DAC appears that ticks all the boxes for me - As part of my vetting experiment tonight I sat and looked at my complete rig (all black) and thought what would a silver Tubadour look like amidst all the other components? Ugly! Sadly my rig is on display in our living room so it would not be aesthetically pleasing. Ah well, first world problems... 

I agree with OP in getting exactly what he wants. Having a I2S input doesn't preclude using and comparing other inputs on same dac. Automatically dismissing any input or interface is nonsense, each dac and streaming setup has to be evaluated on it's own, having a wider choice of inputs makes total sense to me. So far I've compared three dacs with I2S and varying quality usb inputs, I2S has been the winner with all three. 

Seems we have this debate every week. Different streamers and DACs are often optimized for different inputs and outputs, it depends on where the money is spent. I2S and DDCs do a great job of improving the sound of "affordable" DACs and streamers. For example: to this day I still use a Denafrips Pontus II with a Denafrips Iris DDC with a Bluesound Node 130.....and have for a couple of years, and it still works really well. That connection is I2S.

More expensive gear can have other connections optimized: AES/EBU or USB being 2; and in that case there may be no need for a DDC. But to dismiss any connection without trying is also incorrect.

One update: SW1X has replied to me that they will consider customizing a DAC with i2s input configured to my DDC. This may be the winner, stay tuned. I did rule them out initially as being too expensive but they do have a range so this may work out, thanks for the tip Audiogon community! 

Otherwise, since I am mostly happy with the sound of my DDC + Pontus II, I may just throw in the towel on the tube DAC direction and go for a Terminator 15th. From what I've read, and my experience with my Pontus I'll bet I'd be reasonably happy with it. 

Price point of dac may or may not be a consideration as to whether adding ddc is optimal. Adding ddc and it's external clocking needs to be considered on a case by case basis, one can't just assume superior interfaces based solely on price. With ddc via I2S we are directly comparing dac's internal master clock and power supply  to the ddc clock and power supply. Far too many just assume usb is the premiere interface without justification, usb interface leaves much to be desired, ever notice the amount of tweaks, optimizations being offered for this interface. In essence all ddc via I2S is offering is an exchange of master clocks, simple evaluation to determine if one is better than the other.