Room Too Dead

      When I was researching a Home Theater room, I seam to recall an article about how 2 channel listening is more dependent on a balance bawneen reflections and damping whereas an ideal theater room would be very 'dead'. I believe the concept behind this was largely based on a multi-channel setup. Once you get into 5.1, 5.2.1, or 7.2.1, reflections are more likely to confuse the imaging. For 2 channel systems the soundstage, as you are experiencing, is dependent on the right amount of the right reflections. .

     That being said,. I agree with others that pipe and drape may be affecting some mid / high frequencies, but you generally need to get int 4" or 6" rockwool before you start dampening the lower frequencies. It could be that these lower frequencies are passing through the drape, the vapor barrier, and getting nulled by the exposed insulation. If you can get some 1/4" Masonite, cut it up into squares, and start moving it around - hanging from the pipes and attached to sections on the studs, and measuring the results - that would be one approach. My 5.2.1 system and my large 2 channel system live in the same space (the horror). I elected to treat it for 2 channel and ignore the 5.2.1 since that's how I use it 98% of the time. 

@OP. You need to measure the room. An excessively absorptive  room can result in some fairly serious frequency response anomalies. Its more likely to cause suckouts - but the absence of one frequency can seem like an excess of another. A set of test tones and an SPL meter will tell you a lot.

I selected the right product to tame about 90-100 hz and covered with a gauzy, decorative fabric.  .  So yes, insulation can absorb lows if it's what the sound reflects from. 

That’s just mid bass and not what I’d consider “lows.”  The worst bass issues typically occur well below 90Hz — think bass guitar, drums, cello, tuba, lower piano registers, etc.  Around 100Hz you’re looking at things like the lower regions of the electric guitar, tenor sax, male vocals, etc. that don’t tend to cause major issues in most rooms.  Absorptive panels can’t do anything to deal with the lower bass issues that frequently plague listening rooms.

Simple answer:

Diffusers.

My room was too dead to start with with too many absorbers. Adding diffusers at first reflection points made a major difference. Then I kept adding more on back wall and back of sidewalls.

If you had vintage speakers, they would have brilliance (tweeters) and presence (mid driver) level controls, adjustments would perk the frequencies to your liking. They were made because they might end up in a live room, or a dead room, and your particular preferences.

Alas, most modern speakers do not provide level controls

I would start, perhaps finish with a multi-band equalizer

here's an inexpensive rockville 21 band from Amazon (try it, anything can be returned) (they make a 32 band, but enough is enough)

https://www.amazon.com/Rockville-REQ42-B-Equalizer-Spectrum-Analyzer/dp/B00LZDSL7U/ref=asc_df_B00LZDSL7U/?tag=hyprod-20&linkCode=df0&hvadid=312069187648&hvpos=&hvnetw=g&hvrand=13668772867094839483&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9003512&hvtargid=pla-570384384433&th=1

You will learn about your room, specifically what's missing, what boost/cut makes the biggest difference at your listening positions.

For home theater, if the equalizer makes the system sound darn good, I would be done.