Hello there,
first sorry for my english.
I´m trying to connect a QRT5AC and a Litebeam 5AC 2nd Generation. So far, I have not luck! I had tried any possible configuration, including AP/client in both ends and viceversa, but maybe I´m missing something. Please help, any advice here?? Thank you in advanced!

You'll have to post the settings for the devices.

Should be possible using 802.11 protocol.

Litebeam 5AC 2nd Generation

I think on new AC hardware is not possible disable Airmax. There is no posibility connect it (UBNT) with Mikrotik

Litebeam 5AC 2nd Generation

I think on new AC hardware is not possible disable Airmax. There is no posibility connect it (UBNT) with Mikrotik

Read up about it and you are correct, airmax is baked into the hardware apparently.