Olympus E3 Ikelite housing Port and substrobe HELP.

I have recently decided to switch to DSLR underwater photography after 8 years of underwater Point and Shoot photography.
And I have decided to purchase the Ikelite E3 housing.

I would like to house both my 14-54mm and 50mm Marco lenses.
Ikelite recommended 6" dome port #5503.55 Lens less than 4.5" for the 14-54mm.
Ikelite also recommended flat port #5502.41 Lens less than 4.1" for the 50mmMarco.
I was wondering, could I just purchase the 6" dome Port for 14-54mm for both lenses since it could accommodate both lenses?
Would the 6" dome port decrease the sharpness of the 50mm Marco images?

I have a DS51 Substrode from my old Olympus c5060 housing (custom retro fitted) and I intend to buy one more ikelite substrobe for a dual substrobe setup for my E3 housing. I am wondering must I get a same DS51 or could I get a different one such as DS160 and use them together with perhaps a dual sync cord?

Flat ports are recommended for macro lenses as they increase the magnification of the image underwater. A dome port can be used without loss of sharpness, however you sacrifice the magnifying benefit. The #5503.55 is about half an inch longer than the dome port we would recommend for the Zuiko 50mm, but macro lenses are usually forgiving. As long as there is no vignetting (shading in the corners of the images) with that combination you should be fine.

No problem using a DS-51 strobe in conjunction with a DS-160. Use dual sync cord #4103.52 and attach the DS-51 to the secondary end (marked with a red band). Set the electronics switch in the housing to DS-51.

Regards,
Jean / Ikelite
IKELITE Underwater Systems

Thank you very much Jean.
I think I will get the flat port for the Marco afterall, for the benefit of the extra magnification.
Thanks for the clarification on the usage of dual sync cord for DS51 and DS160.