Best transport for USD500

Check with Arcam ... one of my friends moved from the UK to the US, and it was simply a matter of replacing jumpers and switching fuses to convert his Arcam amp and CD from 240V to 110V ... Arcam does a lot of trade both sides of the atlantic, so they might manufacture a single unit for both markets. Transatlantic shipping is another issue, though !

From the reviews I've read the Bel Canto is supposed to reclock the data signal, whereas MSB does not. That should mean that the Bel Canto is significantly less sensitive to the transport. Inexpensive CD players are often not very good transports (poor quality digital out, bad jitter) so I'm not sure the MSB would offer much improvement over say an Arcam CD72 on its own.
There's an audio note CDT-zero on Agon for $600 .... probably a better transport than any of the players you mention. Perhaps you could stretch to a Meridian 500.
Nobody has asked why you're set on going for a two-box player on your relatively limited budget. For the same money you could get a pretty nice one box player. (BTW I have a cheap 3 box setup mission CD-7000 - Monarchy DIP - Monarchy 22A, it cost $400 altogether and wipes the floor with my Marantz CD67SE ... so I'm not saying the multi-box approach is bad, just that it's only one option).
My opinion .. go one box and get an Arcam CD92 with the ring DAC.