If it sounds better to you, it is better.
Generally speaking, the Q150 will benefit from a higher crossover point, especially if you're not just listening at moderate levels. The less the cones are moving, the less distortion. Also you don't have to worry about port noises or the positioning of the port if the speakers don't have to play down to their tuning frequency. With a high enough crossover frequency it might even be beneficial to insert the supplied foam plugs. But ...
... unfortunately, that might not be feasible. With a single mono subwoofer (and the WiiM Amp doesn't support stereo subs) I would not crossover any higher than ~125-150 Hz. This can work
only, if you can place the sub
exactly centered between your main speakers. If it sits somewhere between your speakers, I wouldn't go any higher than ~90-100 Hz. If you must position the sub anywhere outside the main speakers baseline, then 80 Hz or less are generally better. It's probably just too obvious, but the lower the crossover frequency, the less likely it is that the sub can be acoustically located as a separate speaker. But also, the benefits of offloading bass duties from the main speakers and the amp are diminishing.
After what you have done already, the typical setup procedure is to set the phase setting to 0⁰ (sub and amp) and the gain setting to ~50-60% on the sub and to 0 dB on the amp. It's best to only change the sub volume from the WiiM Home App from this point on, if you feel there is too much or too little bass.
Since the Tannoy offers continuous phase adjustment, you should try this out next. Whatever sounds louder is better here. If the result is too much bass from the sub, then reduce the level in the app afterwards. If you have a helper (or even an SPL meter) this job might be a lot easier. If you decide to try a different crossover frequency later on, it just
might be necessary to re-evaluate the best phase setting on the sub, at least with bigger steps.
Now go ahead and listen to some music. The sub should not be dominant in any way. It should just blend with the mains. Adjust the level until you are satisfied. If necessary, repeat with different crossover frequencies.
In addition, your sub also features this LF extension knob. As far as I understand it this is really intended to add more weight to the deepest registers as a special effect (not to make it sound.more natural). The fully anticlockwise position is probably called "Music" for a reason. However, you are still free to experiment with this setting. But this should really be the final step.
