HiFiMan does need to offer more amp boards IMO. I own the standard, balanced, and iem cards. The JH Audio Roxanne and Shure SE530 iem's that I own and have tried with all three cards only allow me to dial up to at most three on the stepped volume attenuator before it's too loud for my hearing. And the volume steps are too spaced such that I find it too loud or not loud enough.
However, my HE-500s, 702 Annies, and Alpha Dogs all play nicely at 4.5 to 6.5 on the stepped volume and there's enough flexibility to dial the volume just right. It's just sensitive iem's that don't play nice with the current amp card offerings IMO. At least as far as the volume control goes. So my solution? I bought the 3.5mm line out cable and hooked it up to my CypherLabs Duet. Ahhh... Now my iems sing. I just wish my 901 cards would have the volume flexibility that the Duet has. Oh well. YMMV.
P.s. I emailed Head-Direct. They said we don't have any plans for new cards in the near future but we will let our engineering department know about your concerns.