Safely combining 2ch. and HT.

I would recommend that you focus all efforts first on the best 2 channel system you can muster and then add a nice dvd player (check out a used Sony DVP s9000es DVD/SACD/CD unit for about $700) and a musical subwoofer. With that approach, you will save lots of $, elbow grease, room asthetics, etc..

If you get the 2 channel right, you're system will be such that most HT systems could not sonically come close to your system and your movies will sound almost as good.

That way you can also sell the Harmon Kardon and upgrade your 2 channel with some better cables, etc..

-IMO

Yeah, the fact that you are going out of your CD players analog output, and into your HK's analog inputs(rerouted from through your 2 channel preamp between them), which might be changing your analog signal back to digital, then back to analog(?...possibly), is surely not going to sound it's best anyway! Even if you're going straight out of your CD player's analog out's, dirrectly into your analog in's on the HK, It's likely still not that good!...as those analog inputs aren't as good as your preamps anway.
Regardless of the "feedback hum/buzz" issue, you should be forgetting about using your 2 channel preamp for what you are trying to do for surround, and just go digital out from your CD playr/DVD player or whatever, and go dirrectly into your Digital input on your HK!!!...just like you wold from you're DVD player! Then, you're still only selecting your "surround in" on your 2 channel preamp, just as before...understand?
I think the fact that you're trying to "feed" into two preamps, is already going to "crud up" the sound fairly bad anyway! However, if you insist doing it the way you are trying to do it(don't understand why, then you can play with "cheater plugs" w/no ground, and that might solve the buzz problem.
So, again, if you occasionally wan't to "process" your 2 channel CD sound into multi channel surround, just go digital out of your cd/DVD player into you're digital input on the HK, and flip the "processor" switch on your 2 ch preamp to let the pre/pro play through to your main speakers, as before. But, trying to go analog out of your CD player into your 2 channel preamp, then out to your pre/pro HK, looping back into your 2 channel preamps "processor loop" isn't going to work well!..infact It's the poorest choice you could do really.
Good luck

May I introduce to you the Sony TA-P9000es? It has absolutely saved my system from having to be divided into 2 systems. If you're not aware of what the TA-P9000es does it is a preamp/component switcher. It has 2 sets of 5.1 inputs for you to hookup a DVD audio or SACD multi-channel player. It has a 2-channel bypass that allows you to hookup your 2-channel preamp to it with the signal passing through untouched. It also has passive 5.1 bypass inputs so that you can hookup your HK up to it so that you can enjoy movies as well.

I have my HK hooked up to it as well as my CD player and TV. I am awaiting a Creek passive pre so that I can hook it up to my 2-channel bypass and then hook my CD player up to the Creek. The Sony is a Stereophile Class A component and is absolutely invisible when you hook up your current components to it. The cost is from $450.00 from Oade Bros. and $550.00 from Onecall. Take a look on Audio Asylum to get an idea of what people are saying about this wonderful piece of gear.

Good Luck

There should be no problem if you use the digital out from your CD player into the HK. Or you can try Y cables from the analog output of your CD player if it only has one pair of analog outs and see how that works. But, if you have a DVD player, it would be easier to play your CDs in it when you want to use surround sound.

Lthkeeper & Rwwear you sound like you or on the right track using the "digital out" on the cdp. If I go out dig.out to the HK "dig. in", the HK surround processor will do it's thing. However, If I also have the Regular Balanced outs going to the pre-amp, I would now be sending a digital signal to the surround processor and an analog signal to the pre-amp which is running the front main speakers. The real problem then is this: Can I also leave the cable hooked up going from the HK "pre-out,fronts" going in the the "surround in" on the pre-amp, which is used when only in HT mode, without causing a dangerous feedback loop? I am assuming that would work as long as the pre-amp is not switched to "surround" mode when playing the cd.?