Tex mix Return A can be configured for line return (it‘s basically a stereo in with simple volume control). Has 1 Master out, 1 configurable ouput (Seperate Bus or Master/ Cue Bus CF) +Headphone out.
Also it‘s a very compact fully expandable mixing solution.
Yes it‘s more than 6hp but it also has your mixing fully covered and won‘t be thrown into the gutter when you expand.
Thank you @JimHowell1970 for the recommendation.
Also dirt cheap. Might suit your needs and even go way beyond.
Edit:
Forgot about direct out‘s expansion which you could also use to go to your main Mixer if you wish.