Power cables for AvantGarde speakers

Do you mean speaker cables?

No, power cables for the Duo subwoofers

You don't mention your budget, might be too expensive, but Townshend Podiums will tighten and extend bass response, much more than any power cord you can find. Read the recent reviews, mine and ozzy,  improved bass is one of the biggest benefits. You will also get much greater detail and imaging, with the speakers disappearing, something power cords will not even be able to touch. But this will not be at the risk of changing the overall character of the speakers like what might happen with interconnects or speaker cables. All the great qualities you like now will be there, only with a lot more clarity, focus, and with greatly improved bass.

Thank you @millercarbon. I have installed IsoAcoustics Gaia 1 isolation stands and i already have all the sonic improvements you mentioned. The bass and imaging are very good in very well recorded records. My feeling or guess is that my next step to try to improve bass quality a little bit could be better power cords. Mine are Furutech power cords, but i think they are also a little long. I’m new with power cords for subwoofers and it’s impossible to just read reviews in other speakers/systems completely different. I could try add your Townshend podiums to listen their impact.

Interconnects and/or speaker cables will bring the biggest change. 

Speaker placement and acoustic treatments will yield the greatest results.

Power cords have a pretty good effect on bass when used on full range components. On subs however, not so much. So I think what happens is the power cord has enough effect on the higher frequencies where our ears are very sensitive that it improves the upper ranges of bass and we hear it as tighter bass all the way down. Similar to the way a super tweeter improves imaging and clarity even though the frequencies are so high we cannot even hear them as individual separate sounds. 

So you can try power cords. Might make a difference, probably depend as much on where the bass amp crosses over as anything else. Or you can try the Podiums, which we already know from guys here who tried both are very similar to but even better than the Gaia. Forget if it was Ozzy or someone else. You can probably find it in one of the two recent review threads. There is a pretty decent price differential, they could probably steer you and help figure out if it'll be worth it or not. All I know, the bass improvement on Podiums is so great that out the window went all my plans for tube traps.

I’ve owned Duos for a long time (with the 225 sub). The trick in my estimation is to get the sub to cohere with the midhorn; that often leaves you with a somewhat bass shy performance. Push the integrated woofers harder and they sound discontinuous. I know Jim Smith has a world of experience in setting these up. I cheated and tuned the integrated woofers as described above, and added a pair of 15" subwoofers and DSP controller for those. The result was more natural transition between the mid to upper bass region, with more grunt and foundation on the bottom.
In terms of power cords, I had a few audiophile brands and eventually bought Kubala-Sosna for the entire system. I only changed out one cable- an interconnect- to a higher grade in their line.
With the integrated sub I did hear a difference, not as profound as with amps (Lamm ML2) or line stage or phono stage.
With the add-on subs, I didn’t bother with any fancy power cable. I roll them off at 55hz. Combined with a change in phono cartridge, from the Airtight line to stone Koetsus, I have a much more dramatic presentation that I find pleasing, listening to a lot of small combo jazz, some rock, and a bit of everything else. Jim would probably tell you placement is more important than the power cord, but the trick with the Duo is that you are pretty much stuck with a position for the whole speaker, not just the integrated woofer. There was a third party stand made by Mapleshade to set up the horns separate from the woofer, but very few units of those were made to my knowledge. I’ve seen them for sale only occasionally here.
Good luck- if you experiment with placement, settings and the like, you can get that speaker to sing, but I think a lot has to do with the associated equipment as well. They can be ruthless in revealing what the upstream components are doing (or not doing well).