There is a comparison between the Rega DAC and the Neko over at the Neko forums.
Transports shouldn't be a problem with the Neko as it has excellent jitter reduction via the Wolfson receiver. I have tried a few with mine and prefer a Sony DVP-S999ES as the transport. It just sounded the best to my ears; I think Sony makes solidly built transports. I also own the 640C and it's very flimsy, I'd avoid using it as a transport if you can.
Transports shouldn't be a problem with the Neko as it has excellent jitter reduction via the Wolfson receiver. I have tried a few with mine and prefer a Sony DVP-S999ES as the transport. It just sounded the best to my ears; I think Sony makes solidly built transports. I also own the 640C and it's very flimsy, I'd avoid using it as a transport if you can.