Benelli M2 question

[comsubin61]

So today I purchased a Benelli M2 used but in fantastic conditions with the 5 rounds tube. I have been doing some research on tube extensions and I can't seem to find one common answer to my question.

Which extension do I use to maximize the number of rounds and have the tube flush with the barrel?

I have looked at Nordic components that seem to have high quality products but there is no informations regarding my question on their web site.

Does anyone know? Can you recommend a product?

Thank you

[comsubin61]

Also as this gun will be used mostly for home defense, unless isis invades us, would you consider an Eotech or something similar? Lights?
I don't want to make to heavy but if it is something that could be needed then I will install it.
Thank you