Double five. My band plays down a half step so it will be Low B flat with a guitar like string next to it. So BEADG with the chorus strings. I'm told there is a 10 str series 2 being built at the moment. I have a cheap 8 str (double 4) Ravenwest and a Hamer 12 (triple 4) That are tuned drop D so this for me will be the highest quality of that idea. Godlyke make a production 10 but they don't do one offs for regular joes. I'm totally addicted to ebony boards and leds and we know who does them on a daily basis.
www.12stringbass.net should give you some internet enjoyment.
Have a great Alembicky day.