How add 3rd CD Player?

I'm currently using my Slink-e & CDJ with 2 Sony CD Players: CDP-CX57 (50+1 CDs) CDP-CX450 (400 CDs)

It's wired for Slink from the Slink-e to the CX450, and from the CX450 to the CX57. The CX450 is the master & the CX57 is the slave.

Audio is wired as CX57 to CX450, and CX450 to the receiver. The receiver is analog audio only.

The 2 players are almost full, so I'll be adding a 3rd CD player soon, probably a CDP-CX400 (400 CDs). What's the best way to wire things at that point, considering both Slink & audio?

An only slightly unrelated question ... is there a problem stacking these CD players, in particular a CDP-CX400 on top of a CDP-CX450?