What is a quick and simple anchor solution on multi-pitch sport routes?
Multi-pitch climbing is where it gets “real"—real good, that is! First of all, make sure your quick and simple belay anchors are redundant. The sliding x on its own is not redundant in sling material: Cut the sling in any one spot and the whole thing unravels. The simplest way to make your sliding x redundant is to tie isolating knots in each of the two arms (seen here). In my opinion, by the time you tie the isolating knots, you've lost the efficiency advantage of the sliding x. I just clip my double-length sling onto each bolt and tie a standard master point knot, similar to this.
As for your original question, just clip both lockers to the slingage. No need for a master point biner in this case. The carabiner holding the greater load will shift to equalize in its direction. But, assuming you are swinging leads, you may not need the second to clip in at all. If quick and simple is your goal, try this sequence to really polish things: Oliver leads the pitch and belays OB (Oliver's Buddy) directly off anchor with auto-blocking device and method. At the anchor, OB remains secure to this device while grabbing the rest of the draws. Oliver takes OB's belay device of OB's harness and sets up to belay OB. OB finishes his or her prep, double checks the new belay device setup now on Oliver's harness, takes the auto-block off the anchor, and climbs on. No need for OB to clip into the anchor.
—Jediah Porter is an AMGA/IFMGA certified mountain guide for Sierra Mountain Guides; read about his guiding exploits at jediahporter.com.