How to change how an Airport Express extends a network

My original setup:

• Coax from Cable company into house
• Cable split in two, one for TVs, other for Internet/phone modem
• Ethernet cable from modem to Time Capsule (latest one w/ 802.11ac)
• Used to use wireless connections to everything.
• But I heard that wired is faster, and I have several fixed devices (latest AppleTV, the TV set, and a PS3) in the living room. So I got an Ethernet switch for the room and ran a cable across the house to connect to the Time Capsule.
• In the basement, I have a eMac and some printers. I connected them to an Airport Express (the latest one that looks like a white AppleTV). The Express connects to the Time Capsule via WiFi.

I heard extending a WiFi with another but using wireless communication for the connection between the primary and secondary device slows everything down. So I thought to buy another long Ethernet cable and connect the Express to the switch.

At first I just connect the Express to the switch without powering off anything. My MacBook Air didn't like the connection. The Airport Connection Utility on the Air still had the dashed line indicating a wireless connection. I unplugged the Express, then the Time Capsule, and replugged them in reverse order. Now the utility shows a solid line (wired connection), but trying to actually use the new WiFi connection is super slow. I unplugged the Express for now.

Is there some sort of setting I need to re-do to get the Express to extend the Time Capsule's network, but using the wired connection between them? Should I do some sort of reset on the Express (or both)?