P.S. Since your amp is class A/B, it will run a little hotter than most other amps - it is nothing to worry about.
I had a Luxman A/B amp and it got too hot to leave your hand on it for longer than a few seconds, so heat is not necessarily a bad thing, but I think you will find using better suited cables will provide better sound and a bit less heat.
As I said above - it is the total capacitance of the cable - so if you have the amp about 3 ft of the speaker then the 12TC should not be an issue. But if your setup requires using cables longer than 10ft I would think about replacing them.
Also - using a heavier gauge speaker cable is not really necessary with a 600 watt amp - UNLESS - your speakers have an impedance of 4 ohm or lower - then a heavier gauge may make a difference.
e.g. my M135 is currently using a cable with a 16 gauge signal conductor. I did compare it to the same cable with a 12 gauge signal conductor and I could not tell any difference.
Another thing I have found helped reduce heat is a better power cable. The ones that Bryston provides with their amps is better than what comes with most amps, but not as good as some third party power cables.
I have observed a drop of 4 Celsius in my Power Node 2, which has an integral 50 watt/channel amp - just be upgrading it’s power cable.
Unfortunately, the build/calibre of your amp would require a very good ($$$) power cable to make any noticeable difference - perhaps something from Nordost. e.g.
- VALHALLA 2 POWER CORD
- VALHALLA 2 SPEAKER CABLE - 10.9 pF/ft
Also checkout their interconnects in the Valhalla range
Nordost is one of the few companies that have managed to keep Capacitance and Inductance of their cables very low (i.e. compared to other brands), which takes a lot of design effort and forward thinking.
I am not an expert on cables, but I have tried a few unusual designs and cable geometries that I found made an observable improvement.
If you are interested in an exceptional DIY cable solution I can provide details for those also.
Regards - Steve