Series = 14 ohms.
Parallel = 3.43 ohms. (Note: 2 8ohm parallel = 4 ohm).
vp150 = 6 ohms
vp160 = 8 ohms
To calculate Series, it's total ohms
6 + 8 = 14 ohms.
To calculate Parallel, it's done this way:
1 / (1/6) + (1/8)
= 1 / (4/24) + (3/24)
= 1 / (7/24)
= 1 / .2916
= 3.43 ohms.
(I've been running my center M2 + VP150 at 3.43 ohm with a Pioneer Elite for months with no problem.)
Just to add, this is calculating nominal impedance, when you start applying an AC sign wave i.e. Music, the resistance's will change, and could result in a lower than the nominal calculated value... I would not hook any speaker or speaker circuit (which you would be doing by wiring the 150+160 in parallel) to a receiver, you would need a pretty beefy amp to handel that load...