That seems like a question that should have been asked before you purchased them. I've got a Z-6 last month that has not run yet. The rear truck was torqued funny and I had to get it replaced. I got the new part but have not yet installed it.
Please let us know how your 8s run when you get them. I've been thinking about getting one of those too.
Unfortunately, as you might know, when one reserves a new brass model, one does so years in advance, sight unseen, and totally on the reputation of the specific builder. Will let you know how they run and sound.
The Z-8 runs as well as the Z-6 and the sound is fantastic. I didn't realize they had twin speaker stereo sound. I love how you can quill the whistle like on a real steam locomotive. I can tell who is operating the loco by just listening to the whistle at a grade crossing. While these don't look as nice as my Division Point locomotives, $1300.00 vs $2500.00 buys a lot of piping. I am impressed enough that I am buying a few more.