Looking to upgrade my 998 at the console. Options are 1 helix 12 si mega or a helix 10 si mega with another helix 10 with just basic 2d and gps. If I went the route of the 2 10" graphs. Could I use the helix 10 si mega transducer for the basic helix 10 for just 2d and mapping or would i need a separate transducer for it.