My first thought would be :

Step 1 - order M80s and either VP150 or (for now) M2 center, keep everything else unchanged except tweaking the speaker levels

Step 2 - big honkin' sub (next year)

Step 3 - replace the surrounds

Step 4 - receiver

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8