Mac Pro early 2009 OS installation

It happened that I had to replace the only hard drive with the new one on my early 2009 Mac Pro. And now I can't install a MacOS on it. As far as I understand, in its basic state (with no upgrade to 5.1 firmware) it would accept only El Capitan. I downloaded it from Apple website and created a bootable USB, but it wouldn't install the OS, saying that it might be corrupted. This is a known issue, so I tried different solutions (re-downloading the installer, creating the usb on MacBook with changed to 2017 date, changing the date before the process of installation on Mac Pro) - but to no avail. Can someone please give me an advice of what should I try next? Much appreciated