Congratulations on the purchase!
Yes, when I mentioned attenuation of the tweeter I was referring to increasing the resistance of R1. This must be tried to understand the difference it makes. It can even make the difference between satisfactory or unsatisfactory low volume listing. It’s one of the perks of DIY speakers building so take advantage of it. Troels usually recommends 3 options. I usually settle on the highest resistance, for my ears and listening environment. You might even find it helps your acoustic issues by reducing treble energy.
Regarding cables, have a read of this link. It is not completely applicable to the Uniti line of products as they are said to be more tolerant of different speaker cables. Although some types of cable are still a solid no, such as litz / woven cable types. When I owned my Atom and switched to Naim speaker cable the change was positive and resulted in greater system balance. Naim amps are designed to work with NACA5 cable. If you can find out the specs of your cables you can work out if they will be appropriate. Also search the forum, there are a million and one topics about cables.
Good luck my friend. Keep us posted.