Orange terror head

You will still need a cab for the orange. There is no way to run two amps into one cab.

 

Bass Terror is a good head, but cab is a big deal since it determines all the important stuff like volume and tone.

 

+1 to both above. You have a combo amp now- if you buy a head, you still need speaker cabs.

 

When you say "Line 6 350w amp", you're referring to the Lowdown combo, yes?

You could connect the Orange head (Terror 500) directly to the Line 6 combo's speaker (bypassing the Line 6 electronics altogether) if the impedance matches. 'TWould involve some spelunking through the innards of your combo and void the warranty...

Don't connect a Terror 1000, it would be too easy to blow out the speaker.

Somebody correct me if I'm wrong.

 

Get the terror head,sell the line 6 and get an 8 ohm cab and in the future you could add another 8 ohm cab and run the head at 4 ohm by flicking the ohm switch over at the back-remember to set the switch to the correct ohmage at the back.
I won,t go in to 2x10,4x10,2x12,1x12,1x 15 and all the variants I,ve missed out that,s another hotly debated area on it,s own.
The terror will run 1 to2 8 ohm cabs or 1 4 ohm cab.
Plenty of advice on ohms on here.
For ohms substitute impedance(edit)

 

The word you are looking for is impedance.

 

The word impedance is my domain.
"I am the biggest impedance known to mankind on bass playing"
Just keeping it simple as that,s what,s on the back-impedance 8 ohm or whatever it is marked on the head/combo and cab.
Anyway get a decent cab with matching impedance and you,ll be good to go.