That 150 mv is
not the pre out spec. It is "analog output" for you to connect to a recording devices etc., but not external power amplifier. The pre out specs are not given in the manual.
It the pre out spec was included, it would likely 1 V, 1.2 V or 2V.
For example, below is for the older DA4ES, 7ES and 333 ES, I have no idea why Sony stopped providing the pre out voltage for some of the newer AVRs, perhaps they were concerned that such specs might confuse people.
In the case of the DA4 ES, 7ES and 333 ES, the pre out specs show 2 V, with load impedance 1 kOhm, that is very good.
View attachment 58396
Typically speaking, when pre out voltage specs are provided, manufacturers don't specify the load conditions but a reasonably assumption is that it is the voltage needed to output the AVR's rated power output. For example, Yamah AVRs are often specified to have pre out voltage 1 V, but we all know they can output much higher, from 1.6 to well above 2.5 V as shown in many of Audioholics.com bench test.