If you really insist on using a relay:

Put your resistor of 68 Ohms between your speaker and the tip-125, and not between speaker and gnd. Put your relay between 68 Ohm resistor and speaker and make it switch between the "output" from your resistor and your ISD chip.....

This will get rid of your resistor when your speaker is connected to your ISD-chip. Whether it is a good solution is another issue...



P.