Switch stacking question

I have a stack of 5 Dell Power Connect 3548 switches that are fully utilized but need more available ports. I have additional 3548's on hand not being used. What's my best option for adding one of my standalone switches to the stack? Would it be simpler for me to set the stack ID to 6 and add it to the stack or could I utilize one port of the existing stack, set proper VLAN tagging and daisy chain to the extra switch as a standalone? Networking isn't a strong point of mine and the ins and outside of managed switches even less so therefore any help would be greatly appreciated