I am going through this same thing right now helping my father-in-law add a second unit to his boat. just like you, he has a Helix 10 SI at his console. I believe he is going to go with another Helix 10 on the bow but with the DI model this time. He is already used to the screen size/resolution and likes it. You said "detail counts for sure".... detail will be better with the Helix 10 over the 9.

Do you currently have the AS GPS HS antenna on your boat? If so, you will either want to get another one for the bow, move an existing one to the bow and maybe add the AS GPS to the transom, just use the internal antenna of each unit, or share the HS antenna with the bow, and accept the extra inaccuracy (which i wouldnt recommend). However, I highly recommend the antenna with heading sensor for fishing off shore structure/cover.

To network the units, you will need 2 of the AS EC QDE ethernet adapter cables. You will also need the ethernet cable, such as the AS EC 20E ethernet cable. You will be able to share waypoints between units. You will NOT be able to share a single map card between both units. You will need a map card for each unit if you use map cards. If you have a AS GPS HS antenna, you CAN share it with both units, BUT.... you will have to share heading AND gps information. You can not share just the heading sensor info with a bow unit on the Helix units.

Joe