Hi,
Unfortunately Google Cast is different than AirPlay, which is more like BT connection where all Phone audio is redirected to connected device

FYI Crossfade control have been passed to receiving device, I suggest that you check Yamaha manual and see if there is an option to enable Gappless/Crossfading playback.

Re Volume Leveling please try with latest MM 5.0.2.2500 build from viewtopic.php?f=30&t=86639&sd=d as e tweaked things a bit regarding Volume level index and casting as bug fix https://www.ventismedia.com/mantis/view.php?id=18132

I use my Android device to cast my Android Library to my various speakers in the house.
I use a few Yamaha MusicCast WXAD-10's plugged in to my various legacy amp/speakers.

With Apple I can cast the whole laptop system using Airplay and this way I can still use crossfade & volume levelling and hear laptop notifications on the cast receiving device. (Not using MM of course!)

I can do the same when casting the whole Android phone but for some reason the connection this uses to cast is really poor, to the point of being unusable.
If I use casting direct from MMA it works fine. I usually cast to Yamaha Musiccast WXAD-10's plugged into my legacy amps around the house. Unfortunately this means that crossfade and track leveling doesn't work.

Is there any way to fix this?

Also is there a way to send notification sounds from MMA to the casting device when casting.
Phone still rings etc but does not come out of the amp , just out of the phone.
I keep missing calls when casting and volume of amp is louder than the phone.