help troubleshooting a grey balance issue?

Hi there, I’m after some guidance on how to go about fixing a colour issue with our printers, a HP Z6100 and a Seiko 64S. I did a search and didn’t manage to find anything that was relevant, apologies if this has been covered elsewhere.

At the moment I am using the US Sheetfed Coated colour space, as the larger gamut helps with Production House 7’s spot colour matching. I am noticing that greys, even plain black greys are printing with magenta cast through them.

Our profiles are built by the folks who service our machines, and although calibrating the head alignment on the Seiko helped slightly, it is still present on both machines.

Would this be a problem with the media profiles or the colour space? Is there a better colourspace for wide format inkjets? Any advice would be appreciated.