I bought the PD before the USB-X Box was released although I was informed about it.
I have been using it with the EVO since then. Also, over the last year, I have been spending increasingly less time listening to music, due to which I haven't thought of upgrading or trying the USB-X.
For someone doing Hi-Rez / DSD, the USB-X is needed.
"Hence would one say that to really take the best out of a PBD Level 5 Dac you would need to spend anywhere from 500 dollars to $2K on a converter."
If you want to do USB, then you need to spend on a Converter. I spent $300 and am very happy with the results and am able to play tracks up to 24/192 without a hitch.
Then again, people spend more on Power Cables, etc. to get the best out of their equipment.
Many are using sound cards that output AES/SPDIF in which case you do not need a converter and can go direct to the MPD.