I wasn't going to comment on this, but the misinformation in some of the above has caused me to reconsider. You have two pair of phono outputs in parallel to each other. You take two pair of cables, only one at a time terminated into the preamp depending upon which is selected. The inductance/capacitance of the unterminated cable in parallel to the signal-carrying cable can definitely influence the behavior of the "working" cable. I've heard this myself so I know that it can happen.
The only way to determine if this is a consideration in your own application is obviously to experiment; it may or may not be an issue.
The only way to determine if this is a consideration in your own application is obviously to experiment; it may or may not be an issue.