See their letter to the PCE linked above. It's not a negotiating stance. For the KKE Palme's Sweden and today's Greece are just "capitalism" and any amelioration of it, is a bonus to the system. It's a binary proposition: you either establish 1 or you're at 0. If you form a coalition against austerity you're "hiding the fact" that austerity is but one tool of capitalism....
It is not incidental that the depiction of SYRIZA as EU apologist has to return to the Maastricht treaty (which 9/11 parties of the SYRIZA coalition were against BTW) because that was the only EU treaty that was voted on before Synaspismos' (the main coalition partner) left turn. They do not mention i.e. that SYRIZA voted against the Lisbon treaty. Because they do not believe in the politics of fronts. It is an open question whether popular pressure might change their minds.

The road of excess leads to the palace of wisdom - William Blake