Have owned pair of 6000's with a 5000 center speaker.

Upgraded to an 861v6, and wondering if I would get a dramatic sonic improvement with a pair of 7200's and a 5200 center channel.

Would appreciate feedback/ recommendations on this move, and whether I should trade the 6000's through the dealer or attempt to sell privately. Is there a market in the USA for used (perfect condition) 6000's and approx what would be a reasonable price to expect?

Thanks

861v6, 800v?, 621, DSP6000s(96/24), 3* DSP5000C Center and Rears, plus a JVC RS50 PJ.