Power cable upgrade for ARC

Wondering if you typically get better results upgrading the power cabling on an ARC preamp or the amp. I don't have the budget to do great cords for both at the moment. I understand trial and error are the best way to find out, but wondering in general terms which piece is more sensitive to power cabling? Both pieces have dedicated A/C lines currently LS17 (15amp) and Ref 110 (20amp) and both are using stock A/C cables directly into dedicated outlets with no power conditioning. Though I do run a PS Audio UPC200 conditioner for my Bryston BDP-1 and BDA-1 digital stuff (also on separate circuit).
A friend has just gone to the mid level Transparent on his Ref 5 and likes it. They are avalable in 20 amp versions. Paragon has a bunch of factory recertified ones at about half price [list $1000] and may still have some.I bought 8 of them so I like them; replaced a mixture of other good cables. See my other threads for more on this.I would do the amp first from my own experence but no way to be really certain without trying it yourself.
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I understood that the 110 at least used detachable AC cords. E. has taken your statement about dedicated A/C lines to mean that they are captive; the Ref 5 is removeable and I had assumed yours were as well so our advice is a little out of sync.
Yes I think we misunderstood each other.

Both of my ARC pieces have detachable AC cables. The LS17 uses a typical 15 amp IEC plug and the Ref 110 uses a 20 amp square plug type.

Any thoughts or experience on which one a cable upgrade is more beneficial to? (speaking in general terms of course).

This would be much easier if both took the same type connecter as I could just try swapping them. Being that they don't, I will need to go through a bit more trouble or buy two of the same cables with different connectors to experiment, if my dealer even has one of each in stock as many times the cables will need to be special ordered (understandable given the current climate, but it doesn't help my cause). I would like to avoid this if at all possible... Trying to avoid the hassle and asking my dealer to accept a return if not totally necessary.
The Voodoo 15 to 20 amp adapter is also a possibility; buy one and a 15 amp cord and try it on both.Leave it on the pre if it sounds better there and put it on the amp if that works better; switching it over to the pre when you feel like investing in another cable.

I have found that the preamp power cord makes more of a difference in my system. I own both an LS25 mk2 and Ref 110.

Audio Research uses Shunyata power cables at shows and in their demo room.
Thank you for all the feedback. After speaking with ARC, I have opted to upgrade the power cable first on my Ref 110 power amp. I bought an RGPC High Tension Wire and am enjoying it - only difference I find is that the sound is overall, moderately faster, no tonal changes, which to me is a good thing. In due time, I will also upgrade the cable to my LS17SE.
Do the amp first, go with the new Shunyata Ztron Cobra....excellent combination with ARC, just can't say enough about it....oops, I see you bought something else already...oh well...lol....moderately faster? should have stayed with the stock if that's the case....good luck!