circuits like that provide actually no serius regulation .... after that if and for any reason there is a bit of load in any of the rails of te preamp will result one rail of 14 volts and one of 15.2 ....dont now how much will effect the sound but still doesnt look nice
Any way i will a agree that those will actually never fail in this circuit ...and also there is no actuall need to look fro subs ,,,any will do as long as is paired with the other ...
regards sakis