The manual there doesn’t say anything other than that the I/O are balanced.
They do note that the I/O are diode-protected; the H90’s I/O are also diode-protected, so you are unlikely to do any damage to either device by connecting them under normal circumstances..
Whether you have signal issues will depend (as always) on many factors, but unless you use very long cables I doubt it will be due to the balanced/unbalanced nature of the I/O. If you practice good signal hygiene, you should be ok.
