would using the onkyo a9150 with Thiel CS6 speakers be safe?

Sure. Why wouldn't it be? Would the Onkyo get the best from the speakers? Probably not. But they should power them fine.

Because the Thiels stay under 4 ohms all the time and the Onkyo only has 60 watts per channel..  I'm afraid of damaging the speakers if the amp was a mismatch or too underpowered.

May work as a stop gap. Not enough info regarding room size and desired volume levels to determine how well.. The impedance of the speakers is troublesome. Sonics will suffer.

I owned CS6 speakers for about 10 years.  The Onkyo could be used a stop gap as mentioned above but I wouldn't play it at ear splitting levels because I'm sure it would clip.  The CS6 needs a high quality powerful amp to sound its best.  Amps that have about 200 or more watts/ch at 8 ohms and double that power at 4 ohms would be a starting point.  I used a Classe SS amp that was rated for 400 w/ch at 8 ohms and 800 w/ch at 4 ohms along with a tube preamp.  If I had to do it over again, I'd probably go with a different SS amp and a slightly warm tube preamp.

Thank you for your answers. With great fear i badly shoehorned my Nordost Valhalla cables into the too tight area and the posts are slightly too wide to get a complete fit (which scared me)  I hooked my Dac up into the Mains In and nearly had a heart attack because some set-up called Direct button disabled the volume n on the integrated amp and allowed the full volume of the Dac to come roaring through.  I ran to the computer to pause the music and then lowered the Dac volume to about 40 from 100.  I think I could go to a line in and that would allow the integrated volume knob to work.  I'm praying that i didn't damage the tweeters...it was horrible sound when that happened.  I own a Krell FPB with the KCT preamp but for the umpteenth time the amp is going back for repair due to shutdown failure.  I am going to very careful with the volume with this set-up.

I have an A-9050, it's 75 wpc vs the A-9150 65wpc. I have it hooked up to Moth Audio single driver speakers and it runs out of gas pretty quick. A Musical Fidelity M3si has way more guts, the M5si would be even better. 

Sure, I'm just trying to play my thiels versus my goodwill stereo instead.  I just didn't want to damage the Thiels.  I am not playing it at any good volume.

I am not playing it at any good volume.

Till you fix your amplifier proceed with that in mind.