Pro-Ject Debut Carbon DC with Ortofon 2M Red Cartridge: BASS sounds 'muddy' The Reason?

I think you should learn to set up your turntable, as is, first, as best as possible .....then decide if you want to drop more money on it, or trade for another. This takes 5 minutes tops.

What is the VTF and Anti Skate set at ?

When you say -

Some tracks sound good and others not so much.

Does the record sound better at the start to the middle, and worse from the middle to the end of the record ?

What stud groove is the anti skate mono filament line sitting in. Is it in the 2nd groove - the middle one ?

From the user manual

https://www.project-audio.com/wp-content/uploads/2018/03/Manual_Debut-Carbon-DC.pdf

See picture on page 4.
Try the line in the first stud groove. Less Anti Skate.

Also what happened when you removed the mat. Did you notice any change ? 

Go from there.

Don't worry about the cartridge for the moment. What’s the table standing on? Try standing it on a sheet of granite, paving slab or thick glass. Is there a dust cover on it? Remove it. Is it in the firing line of the speakers? Stuck in a corner? Acoustic feedback can give muddy bass.
The Denon amp is old and most likely has a crap phono stage. Buy a Schiit Mani from Amazon and plug into an aux input.

LP bass varies from great to awful! Try some of the Sheffield Lab LP's as a reference. Particularly the Track Record.

Just to remind you guys that Ortofon 2M is pre-installed by Pro-Ject on nearly all their turntables/tonearms, so if their arm does not have VTA then a cartridge chosen by manufacturer must be perfect match even without VTA adjustment. User can only adjust Tracking Force and Anti-Skating (they must be the same for this cartridge), that's all. Tonearm is already parallel to the record surface. 

An entry level turntable and cartridge can't surpass proper digital setup, especially if the user get used to digital, not to analog. 



 

+1 noromance! The Schiit Mani, along with a better cartridge (Denon 103R) would be a considerable upgrade! Along with better isolation of the TT. And don't forget the record weight (better coupling of the LP to the platter)!