server board

OK, went to reddit and got my hind handed to me, which I knew was going to happen. So I decided to try elsewhere for help and advice. I wanted to build a home media server for myself. In doing so, I tried an IBM X3550, and that was a bit too slow. Got a Lenovo X3550 M5, much faster AND quieter...

I am building a server platform, although the motherboard has a lot of pcie slots, isn't strong enough to handle multiple gpus if I make it sit vertically(in the usual way) in a cabinet. So I wish to buy a cabinet, which I can sit horizontally, so the gpu's don't stress the mobo. Any suggestion...