I would not be quick to pair ARC and Naim; I can understand why you would have issues. The nature of these two house sounds would not be complementary, imo.
Further, if you are using stock cabling I would assert the weakenesses of each would contribute to quite a tough sound. Using a Vandy 2CE Sig one would not typically expect a thin and strained result, but that certainly could happen with those components and lesser wiring.
My assessment is that if you wish to move quite a distance away from the current sound you will likely need to change both the ARC and the Naim. Individually in properly established systems they can perform fine, but it sounds like you do not care for the result at all, so a sea change is in order. I do not believe that futzing with lesser fixes, i.e. burn in, even cable changes will ameliorate the larger issue. Treatment of the space is also not the issue; you cannot alter a fundamentally poor combination to your ears holistically by room treatment - the character of the system will be only partially ameliorated.
Now, if you do room treatment, cable change, adjust the sub, etc. you may - I say, may - get a nice enough change. However, I feel this is lowered expectations for you. You should use this frustration to seek a sea change in sound, not putz around with getting it "good enough." Seek a FAR higher, more pleasing result, one which will leave you shaking your head at how wonderful it is. Such changes can happen and do all the time. But it will take a changeout of components. If you want a smoother, less fatiguing result, keep the CJ and Vandies and rebuild.
You're doing well to have a forgiving speaker like the Vandy... or else it would be worse! :)
Further, if you are using stock cabling I would assert the weakenesses of each would contribute to quite a tough sound. Using a Vandy 2CE Sig one would not typically expect a thin and strained result, but that certainly could happen with those components and lesser wiring.
My assessment is that if you wish to move quite a distance away from the current sound you will likely need to change both the ARC and the Naim. Individually in properly established systems they can perform fine, but it sounds like you do not care for the result at all, so a sea change is in order. I do not believe that futzing with lesser fixes, i.e. burn in, even cable changes will ameliorate the larger issue. Treatment of the space is also not the issue; you cannot alter a fundamentally poor combination to your ears holistically by room treatment - the character of the system will be only partially ameliorated.
Now, if you do room treatment, cable change, adjust the sub, etc. you may - I say, may - get a nice enough change. However, I feel this is lowered expectations for you. You should use this frustration to seek a sea change in sound, not putz around with getting it "good enough." Seek a FAR higher, more pleasing result, one which will leave you shaking your head at how wonderful it is. Such changes can happen and do all the time. But it will take a changeout of components. If you want a smoother, less fatiguing result, keep the CJ and Vandies and rebuild.
You're doing well to have a forgiving speaker like the Vandy... or else it would be worse! :)