The need for a full range speaker is simply not true. I have a pair of T/9x’s paired with Harbeth 30.2 XDs, stand mounts, rated at 50Hz – 20kHz. They work great! The difference in cost between the 7’s and 9’s isn’t that much, BUT I strongly recommend a stereo pair of RELs. EDIT: Assuming you are mostly interested in stereo audio. 1 is fine if surround sound is the primary application.
You can dial in the crossover to integrate with the main speakers frequency range, whatever that is. The X1’s are rated at 80 Hz – 50 KHz so maybe yours are close?