Any R1900T3 user here?
I want to see the backside of the 2 speakers.

Here are your guides:

1. Go to the car speaker shop and buy a powerful 6.5" woofer and change it with the S4.1 subwoofer. Watt doesn't matter, it just the maximum rating anyway. Anything higher the the S4.1 subwoofer 60W is ok.

2. Change the 35V 4700uF capacitors to 10000uF minimum 35V. I think capacitor's brand doesn't matter much if u just want more bass. (Of course branded is better)

3. Add some sound absorpting cotton or sponge in the subwoofer.

4. Getting a Phillip PSC805 also a good idea, the soundcard bass is strong.
Personally, I don't prefer bass. I'm using PSC805 with my modded S4.1 currently. I moded my S4.1 to get clearer and harder bass and improve the clarity of the mid. Now the LFE of my S4.1 controller need to turn to minimum and lower the bass frequency in equalizer of foobar to get the bass that i prefered while enjoying music. 

I think Edifier S4.1 is built with clarity in mind, it's the clarity the stand out among it's price range.
Have a nice try to unleash the beast of your S4.1 subwoofer.

rioven:

The satelite i already changed the internal wire and the supplied wire, the original internal wire so thin, thiner than the supplied wire connecting satelites and the sub.

For the satelite, i don't know about the caps rating for the tweeter. It written 105K 250V. So I just need to change it to 2.2uF 250V solen caps, right?

I also changed all the caps in the circuits to branded one. The big caps changed to RIFA 6800uF 63V parallel soldered with 0.1uF caps. All the ceramic caps to the plastic type.

The op amp change to OPA2107 for front and bass. OPA2227 for rear.

The subwoofer i changed to Atomic Power Labs, USA 90W cost RM104. That's the best i can get in my area.

I can't find any 3" woofer anywhere to replace the satelite woofer. So, I'll replace the front satelite soon.

I changed all at once, the improvement is significant.
Since hansapkuay is requesting for more bass only, so i think he no need to mod all the part.
xterminator:

If have money to spent, i don't see any problem buying a new speaker. But the improvement that u get from moding, is something u can't buy directly.

Even the new S2.1mkII still have many things that can mod to make it better.