Any cables that give more bass

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

Analysis Plus Oval 9. Definitely a fatter bottom.

Why would a ps audio dliii improve the bass response of his KEF's that only go down to 55hz????? Why would Analysis Plus Oval 9's improve bass response that the speakers can't produce (flatly at any volumne)?

Reference 203 specifications
Design 4 way reflex
Drive units LF: 2 x 165 mm (6 1/2”)
MF: 1 x 165 mm (6 1/2”)
HF: 1 x 25 mm (1”)
SHF: 1 x 19 mm (3/4”)
Frequency response at 15°
horizontally off axis ±3 dB 55 Hz - 55 kHz
LF Corner -6 dB 40 Hz
Crossover frequencies 400Hz, 2.7 kHz, 15 kHz
Amplifier requirements 50 - 200 W
Sensitivity (2.83V/1m) 89 dB
Maximum output 113 dB

If the OP wants to hear punchy bass, the bass line, low organ notes or the tank rumbling into town in Saving Private Ryan...the OP needs a sub-woofer.