CSS is a superset of LD. CSS does what LD does and much more. CSS strengths lay in L5-L7 ie. NBAR, Flash Crowd insurance with WebNS, Cookie and URL inspection, and TCP intercetpt & splicing of connections to the best server in the server farm. Yes it can do L2, L3, L4 but there are other Cisco products to do this.
I agree the inclusion of LD in your new solution limits you to L4 functionality. My own opinion is that a solution is only as good as the "weakest" component. I would go independant of the LD. Perhaps you can redeploy the LD in another part of the LAN?
