Speaker Cables

ProAc speakers have a reputation for being relatively even in response. If you'd like to maintain that honesty I would contact Audio Envy and have them build you a bi-connector set. I believe they're upgrading their SP9 orders to SP11's. The set that they sent me was phenomenal and more even in  response to the point that I no longer used my dirac correction and when I did an impedance sweep it was notably smoother.

Bear in mind that if you put a film capacitors in place of an electrolytic, you will generally be lowering its equivalent series resistance (ESR), and thus altering a fundamental characteristic of the crossover which affects frequency response.

Whether the deviation is sufficient to warrant concern will depend on the speaker in question. One solution is to place a resistor in series with the capacitor to make up the lost resistance. The more capacitors in the crossover, the more significant the issue.

Some people complain that after putting boutique caps in their speakers there are significant gains in transparency, but somehow they sound, ‘all wrong‘. or, ‘completely different‘. Now you have a fair idea why.

thanks again @cakyol @pesky_wabbit @decooney @twoleftears and others for your advice and good points

yes i did check - and the spendor crossovers used high quality box poly capacitors known to stay stable over the years - am glad to stay away from cap replacement given their tricky measured vs listed values, esr’s etc etc - spendor evidently went to great mains to match and select caps way back to their manufacture of the bc1 and successors

tinned ends or solder cups points noted 👍👍

I have been auditioning Kimber Kable’s Bifocals and they sound great - still questioning the dollar value but clearly sound better than other speaker cables in my system. 
Mixed feelings because I was happy using cheaper cables. 

OP, the advice to use 8AWG cable for hook-up wire is simply ridiculous!
I like AWG 21 to 24 solid core pure copper OCC wire for the tweeter with no crimped on terminals anywhere. Solder all connections. If using solid core then provide vibration relief by using cable ties or some hot-melt glue to anchor the wire close to it's termination.

https://www.vhaudio.com/wire.html#vh18hookup : Chris supplies this wire with AirLok insulation which has a very low dielectric constant, even lower than Teflon. I use it inside amps too.

For mids and bass use AWG 14 to 18 OCC copper, avoiding PVC insulation. There are many outlets for good cable.

The advice to contact Audio Envy could work, they are garnering some good reviews. I have not used any of their stuff so have no comment.

With regards to changing capacitors: I do this all the time with great results.
I am sure pesky_wabbit was well-intentioned when he mentioned ESR. This is insignificant in a crossover and can be ignored. In the formula for capacitive reactance there is no 'R" value in the equation.   It is:   Xc =1 divided by (2xPixFxC) If you consider that when caps are chosen for XO duties the closest standard value to the theoretical value is used, then there is the individual driver's response, the overall response and the room's response,you will realise that ESR is a non-issue   : )

Perhaps when rewiring you consider replacing just the cap/s in the tweeter circuit and while you are at if you find any white sand-cast resistors replace them with Mills or similar. Expect a noticeable improvement.