Go balanced or unblanced that is the question

OK. I think that overall having an extra length of cable between the pre-map and amp is a nice thing.no matter the romm rule of thumb will be i would like to keep the elctronics out of the center.So I have a Mac preamp with XLR outs but whose signal path is not truly balanced.Likewise my Mesa Baron has blanced inputs but it's circut topology is not true balced.But because I have an MIT XLR I use as my single ended stuff is lower cost (quality?I don't know!) wire.Also because of a sub output I need the vaiable main out of my main pre out for my sub.The question is should i be converting the signal back and forth?In Hartley's book he say's that converting back and forth cann screw things up.I have alwasy thought that balanced or unbalanced all the way through was the way to go.I might change to a balned pre but like my amp and want to keep it.But if i need to make a 20 ft. run am i better off risking distortion with an RCA or staying with a reasonabley priced XLR from pre to amp?All my sources of course are RCA.Thoughts?
FWIW - I'm running 25' interconnect presently Adcom 750 to Pass Al 5 - unbalanced. No hum or noise problems even if ear next to speaker. However, I live in a rural area so I don't have a lot of EMI or RFI. If I lived in the city I would go balanced with this long cable setup. My CD player is truly balanced and sounds better than when connected s/e, my other components are not balanced and sound good connected s/e. I like the microPurls for 1m s/e component interconnects, IMHO. Nice combination between detail, neutrality, and life.
I generally feel if the component mfg designed the equipment to be run balanced then do so, otherwise single ended is fine. balanced was an original proaudio application to combat signal noise in the lines for the long runs of wire they typically encountered.
XLR balanced cables in general are desighned for the long runs with no noise. Unbalanced though will certainly have greater transparency and details but more hum if you'll go for the long run. I would not advise to use long runs of RCA cables with tube amplifiers on either end.
Several months ago I attempted use a 14 ft. run of unbalanced cable in system. I would get periodic hum, probably from some electrical interference. My preamp and amp both were also equipped for balanced operation. So, I tried it. I didn't have time to go looking for audiophile quality balanced cable. So, I had a company that specializes in building recording studios make me up a set. I have a bi-amped system so I needed three pairs of cables using high quality Neutrik terminators and Mogami cable (total less than $75.00). I was floored by the difference. I can now turn my preamp to full gain and I cann't hear a thing coming from my speakers without a signal: absolutely no hum or hiss. The noise floor was much much lower than with the unbalanced set-up. There is probably a ton of RF interference in my room, and it doesn't phase my system one bit. According to the recording engineer who made the cable, you get more gain and far superior shielding from rf interference with a balanced set up. I also have yet to hear anything to convince me that I need to upgrade my cable. In fact I've taken my amp and preamp to dealers to demo various insanely priced unbalanced cable against my balanced runs, and I have yet to hear any that sound cleaner or better. All things being equal, balanced operation should never sound worse than unbalanced.
marakanetz, another interesting comment from you:

** unbalanced though will certainly have greater transparency and details**

based upon my obervations, i can not agree with this proposition. do you have any experiential or other support for it?

I am running 40 feet of RCA (single ended) from a tube preamp to a tube amp. My system absolutely does not suffer any technical problems from this configuration.

As far as the argument as to single ended being better or worse than balanced, there are too many factors to make a statement based only on that part of the system.
Using a balanced connector from my preamp to my amp gave a welcome 6 db and gave a sharp punchiness to the amp, very tight. It was definitely happier. Then the same cable but with s/e sounds betters from the CD to the pre. It was much smoother and cleaner. This was the best combination for my setup. Dale
i have long runs from pre amp to amps. i use unbalanced without any problem w/noise so long as i keep the interconnect away from transformers etc. i had a buzz when i carelessly stuffed some excess interconnect under the output transformers of my amp (looped it no less!)