wiring question: Here's what I've concluded... but what do I to with the old brown wire connected to T?

old new
W Aux/E
B (blue) not connected
X2 (black) Aux/E
Y Y
G G
O O/B
T (brown) ?
R R (leave jumper in)

x2 and w can't both go to aux, what is brown hooked to in the basement furnace? Blue need to be hooked to c or you wll be changing battries a lot, make sure it is hooked to c on furnace. I would say do not hook black up hook blue to c and white and brown to aux. but we need to see what brown is hooked to in furnace.