Thank you! Got a cold sweat realizing I could have purchased thousands of dollars to waste for not knowing better. Thank you

I see there is an IE44 that adds MMHR. I know what it stands for, but what is it connected to and do I need it if i'm using the HD621?

Sorry for the newby questions, I just feel so helpless. I'm learning tho smile

Meridian 568, Krell KAV 250A2 & 250A3, Oppo BDP 103, M&K 5.1 (S-150 fronts, SS-250 rears, MX-MPS 5410 Pro subwoofer) Sim2 C3Xe PJ, Directv genie