Capacitance problem - long interconnect?

Could a 20 foot interconnect from preamp to power amp cause problems with the highs? My interconnect: Monster M550i
MY take on a preamp not being able to drive a long interconnect is that it's the preamps fault. (or some impedence chemistry between the preamp and amp. BUT a DIFFERENT interconnect might solve the problem. If you can't shorten the connection, try a different brand of interconnect. (I KNOW that could be an expensive mistake)
ALSO: you might find replacing the RCAs on the wire you now have might do it. Try ??? Cardas best silver/ro.. male RCAs. They are like $25 a pair at Welbourne labs, or even any of the Vampire RCAs etc. from $15 or so a pair. The RCAs on Monster are notoriously poor and a new pair of high quality ends might help.. (even replace the female RCAs if that is something you could handle, but not as important as the cable ends)
Elizabeth is right, if the cable you are using is causing a problem, it could be from capacitance it is adding to your preamps output. This effect is the same as adding a capacitor to "roll off" the top frequencies. This occurs only if the measured PF ( picofarads ) total is sufficiently high. I looked for specifications at the Monster Cable web site before posting here. Their advise simply says not to run more than 30 feet. They do not post technical specifications such as the PF per foot measurement of any of their interconnects. If you could borrow something for demo from the Purist Audio line of interconnect, they have very low loss. The inexpensive end of their line ( Elementa) measures something like 17 PF per foot. Even driving a 49K amplifier load with an unbuffered output preamp, this would leave a single ended (RCA based) signal intact at even a 40 foot run.
Sorry, in my original post I neglected to mention that my problems with the highs are NOT with all cd's. Really, they are only with the many 20-year-old cd's I have, most of which were transferred from analog. Even most of my old Telarc's are a problem. I have no problem with any of the
few newer digitally recorded cd's I have purchased (pop and jazz). Two older audiophiles in the used gear retail market disagree on blaming the analog source. Today I gat to try a 25 foot run with very low capacitance (like 7 pf). Will post the results later.