I recently just received my EE DAC and am absolutely loving it!!

Although, as I'm sure most of you understand I'm already thinking about what I can do to squeeze some more performance out of it. It seems like the consensus is that a Mullard CV4003 is the way to go as far as tube rolling goes, and I intend in giving that a shot soon.
I was wondering what some of your opinions are about if it is worth getting an asychronous USB/SPIDF converter instead of using the stock USB (isosynchronous) input. Currently looking into:
1. M2tech hiface
2. halide bridge
3. the new wavelength usb/spdf
I'm not using any high resolution files, so the fact that the EE only does 16/44 is fine with me, I was just wondering if the mere fact that these converters are asynchronous will be an improvement over the stock USB sound. Has anyone done the comparison?