You are using 5m USB cables. Are these passive or active?
Several years ago I came across a 5m active USB 2.0 Extension cable in Poundland and at 1 pound it was was a no brainer to buy one in case I ever had a use for it. I never have.
Ebay (try USB CABLE ACTIVE) has a large selection of them, one even claiming to be USB 3 and supporting 5Gbps data rate.
Might be an alternative, if they work!
Roy.