Audio Amp Circuit - Revised

I am reworking an old Sound Card project and would like to revise the audio amplification circuit. Attached are the old schematic files. I have replaced the AY Sound Generators with an FPGA using PWM output on 2 pins (Left and Right audio) and the new circuit needs to take this in to account. The current design has a Left, Right, and Center channel - same as on the schematic. I'm not sure much is needed to be done with the Center channel circuit, however I am open to changes and you can find details about the circuit online searching "Apple IIe Speaker" or I can supply links to schematics. Currently there seems to be a lot of noise and I want to make the circuit as quiet as possible (within reason). Peak-to-Peak from the FPGA is a bit more than from the AY's and could be part of the issue. The LM1877 is also not the best OpAmp and I would prefer something of better quality. My environment could also be an issue so I plan to use a 4 Layer PCB and cover the audio circuits with an RFI Shield, although you can advise is either are really is needed or not. A Negative Referenced Mixer design is preferred and I think will solve some of the issues as well with mixing. I think part of the noise could be related to the gain needed due to all the resistors to mix the audio. The old design was created by computer guys, not audio guys. Hopefully you can do better than they did. Any questions just ask. Thanks!