What can I do to improve my 2nd system?

start with :

getting better stands for your equipment and speakers

second subwoofer

room treatments

from there you can tweak things

For the speakers, power amp and CD/SACD player, I have attached semisphere rubber isolators (made by 3M) underneath. Would that suffice? But the audio graded stand is definitely good idea.

I had a old sub by Audio Research (AR SW30) and I hooked both of them in stereo mode using the RCA splitter out of DAC. To integrate them together, I experimented several location and found placing both of them inside the L/R speakers is the best location. And I also need to set the phase on the 2nd sub. to "90 degree" to get them better paired together. However, for some reason, the AR sub seems to have hard time to keep up with SVS pacewise. I may need to purchase the same sub. if going for dual.

Here is my curiosity. I understand the 2nd sub is mainly used to mitigate the hump/null and obtain more even low end frequency distribution in the room. Also, having two subs helps headroom for each of them to play more effortlessly. If my seating position is always at the same spot and I was alone listener 99% of time, given the size of my room do I really need a 2nd sub? I was told by SVS tech a single sub. is sufficient given the size of my room. What are "other" advantages having the 2nd sub?

For room treatment, I was thinking placing the bass traps on L/R corners and the sound absorption panels on the 1st reflection points left and right. On the front wall (behind the main speakers), I have difficult time to do sound diffusion because of the windows but, question, may the blinds work as the diffusers (sort of) to my favor? If not, how about thick lining curtain?  What are the right way to treat that?  

It doesn't look too bad. I'd move the loudspeakers to the very front edge of the stands, move the speakers about a foot more away from the side wall, and hang heavy but open drapes.