Bristol_Jonesey

1. Your room isn't big enough for full on bass trapping, so try to arrange it so you have a sofa or other soft furnishings strategically placed, especially the rear wall

Build - fit - measure - test - move

This is an iterative process, hopefully each iteration will get you closer to your goal.

bitflipper

D) Bass traps are difficult to implement properly, nearly impossible in a small room. It is possible to spend a lot of money and effort and still not have effective traps. It is also possible to cause more problems than you solve. Not that you shouldn't employ them, just be prepared for some frustration and don't expect them to solve all your problems.

       
Can I pull your brains regarding room size?

Above quotes refer to the room being too small. I would have an almost double sized room available (unfortunately without this cozy floor heating, that's why I didn't use it in the first place) and would consider moving before starting the "measure, test, move/build" cycle ...

The exact dimensions of the current room are 4.8 x 3.8 x 2.4m, while the larger would be 7.3 x 4.8 x 2.4m, but I'm not sure if it's shape is a disadvantage as there is a part of load-bearing wall extending 1.8m into room, about 1/3 up the long wall size (see sketch below), which I don't know what to do about ...

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  xxxxxxxxxxxxxxxx       cool drawing ;-)

What are you guys thinking? Is it worth moving? Any ideas/suggestions on how to arrange the large room?

Thanks, Colin, for directing me to this link. This looks like a tremendous source for new information! I can see a real fun time coming up, lots of stuff to learn ... and explain to my wife what that all may be good for ....

I will stop bugging guys 'round here with non Sonar related questions, though further comments on this subject are always welcome !

With recording, it's always best to start at the source.  In this case, the room.
 
As was mentioned, move the speakers (your listening position) as far away from the walls as possible.
That'll help a great deal.
 
Essentially, you're looking to damp and diffuse reflections.
Since it sounds like the room is essentially empty (other than your gear), consider adding some large/soft furniture.  A nice over-stuffed Sofa or Futon... and a couple of similar chairs (strategically placed) will make the room more comfortable for guests... and also tame excess ambience.
Normal household items (like bookshelves filled with books of different sizes) can make good sound "diffusers".  Add some of these types of things to the studio area.
Use normal creature comforts (creatively) to make the space comfortable... and more acoustically pleasing.  Once you've done this, if the room acoustics still need improvement, it's time to consider specific acoustic treatment.  It's amazing how far you can get using "normal" items.

I'm using a combination of acoustic treatment (4 gik tritraps, auralex panels) along with the ARC plugin in the control room. The control room isn't as large as I'd like but I've not had any issues with the song transfering as I want when I've taken it to mastering houses. I set up an ARC bus in sonar and route the master bus to this before it goes to the main outputs in sonar (when I bounce the audio to a stereo file I never have the issue of turning it off or forgetting about it).

Given a choice I'd always choose acoustic treatment over the correction software but it can help a treated room.