You have not specified why you want to test this modified culture. Rather than that, we have Brain heart infusion agar also. You can try that. If you want to test for antimicrobial susceptibility you can use mueller-hinton agar supplemented with 5-10% sheep blood.
It is not clear why you need to mix the two culture media? Brain Heart Infusion Agar supplemented with 5-10% sheep or horse bloods is quite suitable for cultivation of most streptococci strains in an atmosphere with 5% CO 2 for two days.