Unlikely at 70; and Probably Unlikely even above that - although don't recall right now what the "max" volume setting is on the ST50.
You SHOULD be able to hear Distortion begin to creep into the audio if you are driving either the speakers or the amplifier too high: at THAT point, it would be wise to dial the setting back somewhat!
And - as I believe someone else has pointed out - "70" is just a number: Pan could re-calibrate their volume reading so that the same "loudness" would only register "50" - or even "20"!
A lot of owners used to think they had a Powerful Amp if the Rotary Volume Control blasted their ears at Position 1 (of, say, 10), and would buy that amp over another that only reached the same apparent loudness on a setting of "5" or "6," even though the rated output specs were similar. In truth, the more likely scenario was that the manufacturer of the first AMP simply chose a high ramp-up for their vol control (perhaps with their Target Market in mind....), and thus sacrificed Fine Control at lower volume settings...
In any event, we have often ran Pan plasmas at Nearly their "full volume" setting, and haven't had any blow up on us yet.
Even so, because the ST50 is still so new, if I find myself tempted to push much beyond "70" will simply give up & turn the HTR on - but that seems a "waste" for morning exercises...