Running both Magnum 350 & Fluval 404 on a 180 gallons planted tank

[Toffee]

Can Any one help me with this:

I have a Magnum 350 & Fluval 404, I would like to use them on a newly
acquired 180 gallons (6'x2'x2') tank with built in overflow I am thinking
of doing the following, which one is more feasible?

Option 1.
Overflow > buffer container (5 gallons?)
both 350 & 404 suck from buffer and pump back to tank.

Option 2
Overflow > buffer container
350 sucks from buffer and pump to buffer container #2
404 sucks from buffer #2 and pump back to tank
(using 350 as a mechanical & 404 as bio)

Option 3
Overflow direct connect (pipe>adaptor>hose) to 350
350 direct connect (hose>adaptor>hose) to 404
404 to tank
(will this setup hurt the motors of 350 & 404?)

This tank will be fairly heavily planted.

Any advise is appreciated.

Thanks

[jet]

Option 1. Maximizes the filter's through put and the rate at which the
tank is circulated.

Option 2. What is there to prevent buffer #2 from overflowing if the
Magnum out pumps the Fluval or from emptying if the opposite is true?

Option 3. Connecting fluid pumps in series is tricky. If done correctly
the output pressure is increased although flow is not (other than from
the increased ability to overcome head). If not done correctly there is
a chance of one of the pumps either cavitating or just being forced
along by the flow. Either would reduce the effectiveness of the system.

So option 1 is your best bet.