Twelve meters is a bit long for line level in unbalanced interconnects; there will some signal loss. Any chance you have a balanced option on your preamp to amp? Otherwise, in general and in my experience, it is better to keep unbalanced IC length short and go with length in the speaker cables. Obviously, you likely have spacial requirements not fully explained here so my comments are conditional.
Interconnect Cable Length
Quick question - I have a preamp with 75 ohm output impedance and an amp with 47K ohm input impedance. What would be the maximum length of interconnects I could use between them without sacrificing sound quality? I know the answer will depend on the quality of the interconnects but I'm trying to work within a $200 budget, if at all possible. For example, I see the AudioQuest Evergreen cables sell for ~$120 for a 12 meter length. Also, is there a general rule of thumb for trade off between speaker cable length and interconnect length, assuming comparable quality cables?
Thanks in advance.