I was wondering, do I really need to purchase some "boutique" eurorack module to do the 5v to line conversion.
And could I perhaps get some normal audio mixer and use some adapters on it?
-- soundmodel

Neither Ladik nor Doepfer are "boutique"; they are at the lower end as far as pricing.
I guess you could use a mixer with a -20 db pad on the input.

Know someone with some electronics knowledge?