You have discovered one of the issues of listening to music on an Alexa device, i.e. they are single track playing devices for the most part, not for symphonies, unless there is a trick I am unaware of.
I only have the basic free music from Amazon, since I have a lot of collected music already, but it might be possible to select a complete symphony through the Amazon Music app
Anyway, if I want to hear symphonies, the last place I would listen to them on would be from any type of Alexa device -- I would play one from my collection on a CD or digital file on my nice stereo system.