Hi Steve,
Really interesting thread guys.
I always dreamed of having an isolation booth to put my turntable in but until the advent of standalone phono stages that wasn't really practical. Now I could see that have a phono stage with balanced outputs could get the table far enough away so that any mechanical feedback would be eliminated.
Myself, I sit as far away from the speakers as possible. I have the turntable and preamp close to me, and the power amp or amps close to the speakers. In my experience, the long interconnect between the preamp and power amp does not degrade quality, but having the turntable and preamp as far away from the speakers as possible on one hand, and having as short a speaker cable as possible on the other, makes for a significant improvement.
At line level, and at the kind of cable length we're talking about here - enough to get across a room - unbalanced inputs and outputs are OK. Balanced interfaces do offer advantages, but having unbalanced interfaces wouldn't stop me from running long interconnects in my room - in fact that's what I do, I have seven metres between my preamp and power amp and everything is unbalanced.
You do need to watch the output impedance, though. Anything below 1k is OK to drive up to twenty metres (sixty feet) of cable of 100pF/m capacitance (30pF/foot) and get a -3dB bandwidth of 80kHz. An increase of cable length, or of output impedance, or of cable capacitance per unit length, decreases the bandwidth proportionally.
If you want the advantages of balanced interfaces, I hold that you can get most of them by driving a balanced input from a single-ended output if they are interfaced properly. The other way around - balanced output into single-ended input - does also get you some of the advantages, but not nearly as many as when driving a balanced input from a properly interfaced single-ended output. Of course, driving a balanced input from a balanced source is the optimum in terms of interfacing, but the balancing at the source end of things is the icing on the cake, and not the cake itself, especially at line level, in my humble opinion.
So it's not actually necessary to upgrade all your sources to balanced outputs to reap most of the advantages. I consider that the most bang for the buck when going for balanced interfaces is a preamp with balanced inputs - that will give most of the advantages of balanced interfaces with all your sources, single-ended or balanced. Also a power amp with balanced inputs will get you most of the advantages of balanced interfaces when driven by any preamp. I consider balanced outputs from the sources to be the last priority.
So I suggest that, if you're interested in balanced interfaces, having balanced outputs from your phono stage is lower in priority than having balanced inputs on your preamp or whatever else the phono stage will be feeding.
Best regards,