wireless rears

okay i have a sony 5.1 system from the late 90's. its like a save 59 or something. The problem is everything works awesome except for the rear speakers. the speakershave an svideo cable in the back which is for the infared sender which is recieved by the rear speakers. The problem is that they suck, they crackle and about after an half hour the left rear goes out. the problem is that i have no way to connect new rear speakers and no other new ones will match up...got any ideas on what to do besides buy a new system. i think it sends on 900mhz

If it uses an infra red sender, it's not 900 mhz, which is RF.

so is there anyway?

That's the problem with some all in ones, particularly when they use "one off" technology..

They may be attractive and iinnovative when they work but when problems arise, service and/or replacement parts can be difficult or impossible to come by.