The Quiklok MKS4-ARM extension can be added to the MKS4 keyboard stand, giving you two extra arms with a maximum load bearing capacity of 20kg.
The Quiklok Z-727 second-tier supports enable you to add a second tier to your Quiklok WS550 keyboard stand in combination with the WS562 bar.
Got an X-style keyboard stand from Quicklok that you want to expand so it can take a second keyboard? All you need is the Quiklok QLX3.