i am having difficulty with mask "breakout and a sore nose bridge.  i am looking at pillow masks and i am wondering if most masks are interchangeable with the different machines .... particularly resmed and remstar

All of the CPAP masks and hoses are interchangeable with different brands of CPAP machines and hoses.  

The only possible issue I know of is that if you use a ResMed mask with a ResMed machine, some machines will display the leak rate minus the typical mask exhaust rate for the model of mask that you are using; if you use another brand of mask, the machine will display the total leak rate without compensating for the mask exhaust.

Have you talked to your Clinician the person from your DME company that set you up with your cpap and mask that your having this problem? 2 things you could be tightening the headgear to much or the mask could be to small. Don't be afraid to call your DME untill you get what you need!