Last month, I heard the second installment of Anthony De Mare’s Liasons: Re-Imagining Sondheim from the Piano project at Sheen Center. De Mare has commissioned dozens of composers to fashion arrangements of Sondheim songs. The results are as fascinating as they are eclectic. On Thursday at Symphony Space, De Mare completes his live presentations of the commissions with a third concert. Among the featured composers are Steve Reich, David Rakowski, Paul Moravec, and Duncan Sheik. The concluding arrangement is by De Mare himself: “Sunday in the Park – Passages.” Sondheim will be on hand and the ECM recording, a 3-CD