what is my system's weakest link?

Hi,
I have put together and entry level system, and have been enjoying it for a while now and feel it might be time to step it up and upgrade.

My system consists of:
Thiel cs 1.5 speakers
rega brio-r integrated amp
pro ject debut III Turntable

I use my system for playing records almost exclusively

What component should I switch out/upgrade first?

I have been looking into Mcintosh c28 preamps as an option to switch my integrated with, had a chance to listen to a system with that c28 preamp and it sounded great , warm and very detailed, and it seems to be quite affordable

Any way any advice or tips on what my next move should be regarding new equipment that is relatively affordable ($600-$1300 price range) would be appreciated

thanks
Morey