I'm paraphrasing, so please bear with me here -
James has said the differences between the two aren't performance based. They're connectivity based. I think the main reason why people go from the BP6 to the BP16 is connectivity - more inputs and outputs, ablilty to have an internal DAC and phono stage together, and so on.
What you're saying about sonics makes sense on paper. If everything is shielded and powered correctly, there shouldn't be a difference though. Bryston takes their time and does their homework when designing stuff, so I doubt the sound quality suffers with more stuff in the same chassis.