Hi,
 
Is it possible to have multiple instances of the Pro-channel Parametric EQ in one channel strip?  Or does CW have another LOW-cpu alternative so I can slot a second parametric EQ in a channel at the end?
 
I do a high-pass at the beginning of my high-bass channels to prevent mudding with the sub but some effect boost residual bass again which I need to filter again...

No and yes. You can use Sonitus EQ or the LP EQ  as a second EQ just don'rt use it in LP mode

Unfortunately Sonitus does not have a low cut.  I'll have to stick with the Fabfilter I bought - it seriously eats CPU if I have a few of them...

Sonitus has a low shelf and high pass filter. It is also possible to stack high pass filters to get an extreme low cut if needed. The LP EQ is another option as mentioned above set the Precision to nonlinear in the expert settings. Kind of surprising you are experiencing heavy CPU usage from Pro-Q2.

Why not use whichever one you like best and freeze the track?

RedSkyRoad
Unfortunately Sonitus does not have a low cut.  I'll have to stick with the Fabfilter I bought - it seriously eats CPU if I have a few of them...

Check out Week 57 in Friday's Tip of the Week for info on how to stack Sonitus EQ low cut filters to create super-sharp cutoffs.
 
I need 8 ProChannel stages sometimes when mastering. If you want to put two Pro Channels in series you have a few options, like sending one track into another track via patch points, or sending into a bus. 

If you need multiple ProChannel EQs, you can utilize AUX tracks.
Create aux track and route your original track there. Now you have two EQs available.

RedSkyRoad
I do a high-pass at the beginning of my high-bass channels to prevent mudding with the sub but some effect boost residual bass again which I need to filter again...

Did you try BOZ Bark of Dog ?
 
If you just need a low cut that may be it. Works fine, doesn't take much space / CPU and has the resonance option.
 
Apart from that I would just stick the preferred EQ into an FX chain and only map the 1st band for low cut.