Seems that there are lots of us currently doing tower systems. I was going to do a group buy for this but it didn't really seem worth it just to save a couple bucks so I just thought I would pass this information along.
I just ordered a wiring harness with disconnect ends from Audiopile. They are making up two for me and a friend. I used their cable in the past and really liked it so I ordered more for my next boat (in anticipation). The cable is heavy duty black pro-audio grade 13ga wire with genuine Neutrik NLT4-BAG/NLM4-BAG cord ends. The ends are $10 each and the cable is $0.50 per foot assembled. They also sell 11ga wire (it's european 4 sq. mm wire that's why the odd measurement) but it cost $1.04/foot. I will be getting a sample to check it out.
I ordered mine 30' long so I will have plenty to go all the way to the amps. They cost $35 each plus about $8 shipping.
Give them a call: 509-287-2020
Here is a link to the cable:
http://www.audiopile.net/products/Speaker_Cables/NL-4_speaker_cable/NL413_cutsheet.htm Here is a link to the ends:
http://www.audiopile.net/products/Adaptors_Connectors/Neutrik/NL4_Speakon/NLT4MX-BAG/NLT4MX-BAG_cutsheet.asp If you want to use the panelmount on your boat you can use the clunkier cheaper NL4FC end and save yourself another $12, these are not as strong as the M series ends.