I wish I had done a search through this forum before wasting hours of my time and PS Audio staff time.
It did reveal, however, that technical support staff needs to read the forums and be better informed of customer issues and solutions. The manual may also need a minor correction.
I called after noticing a hiss on my speakers that did not exist with any of the previous DACs I had used. Troubleshooting pointed to a defective DS Senior being the culprit since switching to any of three other DACs produced no speaker hiss. The possibility that the attenuator could play a role was not mentioned.
Had I read this forum sooner I would have known the purpose of the attenuator, particularly when directly driving the BHK 250 and 93db sensitivity speakers. My problem would have been solved. Engaging the attenuator completely eliminated the hiss on the tweeter and lower frequency noise from the midrange and woofers.
I went through many troubleshooting steps, including changing just about every component to no avail. A very careful reading of the manual might have given me a clue, although I would recommend the manual include sensitive speakers specifically in the language:
[If the power amplifier, preamplifier, [edit: or speakers are] overly sensitive or you need to reduce the output level of DirectStream for any reason, you can activate the output attenuator to reach a lower level. There should be no sonic penalty for doing so.]
Stating “or you need to reduce the output level of DS for any reason” may cover speakers for the writer but it did not for me.
I feared that engaging the attenuator would reduce SQ but reading the forum eliminated those fears. I was running my volume control (attenuator disengaged) between 50 and 70 depending on musical content. Ted gave a 60 level as a guideline threshold and my use lies below and above that threshold. I do not think it matters to SQ since engaging the attenuator eliminates my noise problem. Please correct me if that is not the case. I do not use a preamp and drive the BHK 250 directly from the DAC.
There are many good explanations in the forum as to how the attenuator works and plenty of guidance to follow. Thanks to Ted and others who contributed so generously.
P.S. My equipment is computer, P15 power plant, DSD, BHK250 and Focal 1038 Be speakers.