Help speaker loading proplem

Hello,
My 3way Diy speaker is using
Tweeter 6ohm
Mid 6ohm
Bass parallel 2x6ohm @3 ohm
Passive crossover and running time is almost 3years .withen three years
I got problem
1: bass one driver damage
2: using bi amp and bass power amp blow
3: another bass driver damage
4 : last week one tube power amp also damage
I carefully thinking problem isall time from low past driver .
6ohm driver parallel 3ohm loading any effect for power amp or driver .
Can I need to change series instead of parallel?
Pls help me .