Pops can happen when a DAC switches from one sample rate to another. You can use MC's DSP Studio > Output Settings to resample everything to one rate. Buffer size is another possibility.
Are you using DLNA? If so, try connecting directly to the DAC instead. You should be able to get gapless playback.
He is using Gizmo to cast to a Chromecast. None of what you wrote is relevant to his set up. MC's DSP Studio is not active in this scenario and buffer size has nothing to do with it. He already explained he is not using DLNA.
OP: Gizmo casts using the settings within Gizmo. If you want to mess with any settings, you can mess with those. There is no sample rate change going on (all audio is being sent at whatever mp3 setting you have selected in Gizmo Audio Quality) so I'm not sure what is causing the clicks/pops. You can try setting it to Low 64kbps to see if that helps with transitioning/lack of response.
(PS: As an aside, I'm not sure how "much better the music is" compared to your old set-up. At best you are only sending a 320kbps mp3 stream. There is no magic here).
In general though, I think what you are running into is the limitations of casting. It is slow to respond and frequently lags. I have found it to be a cool party trick where you can be like "hey, check out how I can send this ONE song to the TV." It plays, then you move on to other things. Its slow response, issues with seeking, and often disconnection do not make it a viable solution for an sort of consistent, long term playback. My Chromecast has been sitting in closet somewhere for a couple years now.