Maximum input power?

[KK6JR]

I take to heart the many warnings not to present too much power at the RF input port (such as parasitics from a nearby transmitter), and the specification at http://sdrplay.com/docs/SDRplay_Technic ... n_r1p4.pdf
is not too helpful in that it says:

The SDRplay RSP is a powerful wideband full featured SDR which covers all frequencies from 100KHz up to 2 GHz.

Yes, I get that it's powerful. But just how powerful?!

What is the maximum allowed input without risk of damage to the front end of the SDRplay?
Better yet, where is it documented?

I want to connect the output from a HackRF One to the input of an SDRplay and need to know how much attenuation in needed.
The maximum values for the HackRF One is 15dBm out and -5dBm in (signals below 1GHz). So to connect two HackRF Ones I would use a 20dB attenuator.