Ray, I'm curious as to why you think you'd have to get rid of your Birds to put LS on your boat ??
I have a Hook 7 at the bow right now & if I added LS I would keep it where it is and use it for chart maps/waypoints (tdx is on the TM). The LS tdx would be on the TM shaft ... black box would be on the deck ... Garmin unit would be mounted on a Cumberland Crappie adjustable mount. At least that's the plan I have in my head. My buddy has LS and has a similar setup ... and his "other" unit is not a Garmin. He has his other unit set on split screen ... 2d sonar / map with tracks and waypoints showing.
Maybe I'm interpreting what you're saying wrong, but it sounds like you're thinking you'd have to have all Garmin units