Any cables that give more bass

that's not a problem....many subs have line level inputs...you wire your left and right amp outputs thru the sub and then the crossover in the sub feeds the non supb output to your speakers.

Xlo speaker cables are known to improve strong on the bass, but they are expensive. Bass traps will weaken the bass even more-so forget about those. How close are the speakers to your rear wall? The closer the more bass you will get!

I would also look at a solution other than playing with cables.

The KEF 203 is rated down to 55hz. I would run a sub no higher than 60hz or so. The natural rolloff of the KEF's would make it unnecessary to insert a highpass filter before the amp to drive the KEFs.

.....you wire your left and right amp outputs thru the sub and then the crossover in the sub feeds the non supb output to your speakers.

There's too much to be lost by running your signal through a subwoofer that then will drive the main amp to the main speakers. I would try every other option before this.

Does your integrated amp have line output and power amp input connections? Can you use these and still retain the link between the internal pre and power amp sections? If so, you could run a line level IC to the powered sub and be done with it. This would allow the KEY to run in its current configuration.

With some integrated amps the pre/power link is broken if a cable is plugged into the line out or main amp in. If so, you could use a Y-adaptor off one of the line outputs, either L or R, and drive an IC jumper back to that amp input and run a longer IC to the powered sub's line input.

With the "right" level setting on the sub, this could be a very nice result. I did a similar task for a friend who has simple Polk speakers and the result with the sub was quite impressive.

i try to move speaker closer to rear wall and about 7inch now and did improve the low,hmm like it,thank arned