Advice on Speaker upgrade vs System Component Upgrade

I suggest you add the second woofer before you do room treatments.

A stereo pair of subs is a very different experience than 1.

I would upgrade your speaker to a floor stander which will have better frequency integration than an sat/sub. brand is your preference.  I love Wilson.  Just upgraded from Alexia (with two subs) to Alexx V (no sub) and realized big SQ improvements.

I have seen your Room Dimensions and a proportion of your Rooms Layout.

I would not be too hasty to focus on controlling Bass Energy, the Deep Pile Carpet is already absorbing energy from the lower frequencies.

I feel based on my own experience of working in a smaller space that working with the energy in the room and diffusing it, can prove to be the best starting place.

Hearing Sound that is not a reflected sound can be appealing with immediacy.

How the sound is managed is a evolving experience, more can be attained as the ear learns more of what is an attraction.     

square rooms are difficult

So thanks again for all the help - what a great community!

I have been leaning Sonus Faber for a long time now, and thanks @skchun for pointing me at the Guarneri Evolutions on TMR - i had a think, and for that price point, I decided to pull the trigger.

Beautiful speakers, and I love that SF sound. They are well reviewed, and should be a next step up in quality... or at the very least a different sonic character to the Dynaudios that i know that i love. They also apparently sound good at low listening levels which is important to me as i do most listening late night. Finally, if they don't work out, they will have definite resale/trade in value, or could sell the HS (but i love them and won't sell unless i have a very good reason) 

They should work in my small room better than a floor stander (i'm just not convinced I can ever make that work in my room really well). I have an old pair of B&W CM10 S2's that i had in there and had trouble with bass - I certainly preferred the HS + Sub as i could keep the bass levels down at night, though the HS are a better speaker all around so not really fair.

These will also benefit from the treatment i'm going to do (gik acoustic or auralex). Again I don't really have a "boomy" room with the carpet, curtains and closet in the office room, so i'll start with some diffusers on side wall and behind listening position and go from there.

I'll be able to directly compare them to my Heritage Specials and see which i prefer in the room. I also think that I will have the option to move them to the living room if that's where they end up sounding best, but I won't be in a hurry to do that - they will get way more use in my office/listening room.

I'm pretty sure that the next purchase would be a good tube amp with more grunt and quality than my Wilsenton R8 (nice as that is for the price)... So i'll throw that bone out there to the group...

I'm also pretty sure i'll add a second sub for the stereo pair at some point. 

Thanks again for the support and advice - very much appreciated!

Happy Listening!