From the manual:

I've been searching high and low to no avail -- what are the output specifications of the phone output and at what impendance?
I saw that using te filter option it gives heavy spikes on the audio -- causing one side of my phones to blow up.
The phones I used were not ratedfor high input so that may have contribted to it but having phones level at 1/4 and blowing up one side was kind of "surprising".
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From the manual:

thx. I checked the pdf and looked for the corresponding output power in mW instead....
I'll see if I can convert to mWatts into 32 Ohm and post here as a reference.
OK,
took some time to get back the stuff in my head (30+ years ago at school...)
+8.5dBu (0 dBu is 0.775VRMS) means approximately 2.06VRMS. In 32 Ohms it would be around 130 mW.
With the phone specs of the RPDJ1210, it would mean approximately 127dbSPL max.
(I do wear in ear filters by the way; the frequency response of my ears are measured and they are on par with someone of 25 ... 30 YO)
@Roeland > Have we addressed all your questions in this thread?
you did and afaik I also cannot add anything else useful ;-) So to answer the -not-asked-question : yeps, it can be closed ;-)
Cool, thanks.