2 channel tube preamp for a HT receiver?

I would like to improve the sound of a Harman Kardon AVR7000 receiver, connecting the CD and turntable to a 2-channel tube pre-amp and then to the receiver, for using the receiver just as an amp for stereo music, and keep the DVD connected to the receiver and 5.1 channels for DVD and Homecinema.
I have Dynaudio speakers (4 ohm - 87 db) so I need lots of amp current to drive them.
The receiver has 5 amp outputs and 5 preamp inputs (2 front, 2 rear and 1 center), interconnected with an external switch, as if the two sections of the receiver, amp - preamp, were internally separated and externally connected with that switch.
I thought to connect the 2-ch outputs of the preamp to the front channel preamp inputs of the receiver, but I doubt if, this way, I shall loose the front channels for DVD playing ( the DVD is connected to the receiver).
I also thought to connect the preamp to a L-R line input of the receiver, video 2 for example, and keep the receiver amp-preamp sections, but I think that this this way I will not get much improvement.
Do you think I can get noticeable sound improvement doing this way, or I am wasting my money?
How can I connect the preamp and the receiver?
Connect the front L/R outputs of the reciever to an Aux or Video input of the tube preamp. Then connect the preamp outputs back to the receiver. Set the volume on the preamp to 12noon and balance the output of the receiver to that for 5 channel use. You could then use either the receiver or the preamp volume knob to control 2 channel volume.

That said, I doubt you'll get much of an improvement from doing this as you are more or less just layering two preamp sections on top of each other. If you have a separate preamp/amp combo for the two front channels then reuse the receiver for the other three channels then you have a nice purist path to the main speakers and a slightly degraded signal in the front for 5 channel use.

Hope this makes some sense.
Try this thread--http://forum.audiogon.com/cgi-bin/fr.pl?bhome&1033239358&openusid&zzEdesilva&4&5#Edesilva

One concept is use one set of DVD outputs to go to 2CH preamp, and the other set to go to HT Rcvr. The FR/FL pre-outs from the HT Rcvr can then be run back thru 2CH preamp. Requires adjusting 2CH pre to preset volume to match HT surround volumes, but something like that might work for you.

Using this setup, for 2CH audio, its DVD->2CH Pre->Spkrs. For HT, the DVD runs through both the HT Rcvr & the 2CH Pre, but sound quality there probably isn't as much an issue...
it is much simplier to browse a used market for Plinius 8200 integrated 175W/ch amp and build a separate 2ch than strangle yourself with receiver setup.
there also more powerful integrated amps for a budget price on the market that will bring you much more performance.
With your current set-up and an additional pair of high quality interconnects, you can interface the tube pre-amp with your AVR 7000 using the using the front L/R channels of the 5.1 inputs reserved for external processors. You can do this using either the pre-amp outputs OR the tape output loop IF it monitors the function switch. The latter allows you to use the HK's volume control solely, and the former gives you more vlume adjustment flexibility & probably better sound. Just be careful not to overload the HK's inputs by setting the volume control too high. You'll have to play it by ear (pun intended) :-)
Tpao--wouldn't that run the 2CH signal through, effectively, two preamps? In other words, signal goes in the AVR then to the tube pre, then back to the AVR, then to the amps, no? If the goal is better sound, I like the concept of using a second set of outputs from the CD/DVD (the other set goes to AVR; e.g., digital coax to AVR, analog coax to tube pre) going into the tube pre, and then running the L/R front from the AVR to the aux inputs of the of the tube pre. This means you have a cleaner path--CD/DVD->tube pre->amps for the 2CH high quality audio, and a slightly more complex path for front L/R for the lower quality HT--CD/DVD->AVR->tube pre->amps.
Edesilva, yes, you're right, the more direct path from pre-amp to amp, the cleaner and ostensibly higher-quality sound. What may be somewhat confusing is the external switch mentioned between the receiver's pre-amp outputs and the internal amplifier inputs. However, my chosen path would allow the user to switch between sources already connected to the receiver--retaining all of the receiver's 5.1 capabilities--and the tube pre-amp (and whatever is connected to it) simply by connecting the tube pre-amp to the L/R main inputs of the rear 6 channel external processor jacks. I believe these jacks bypass the built-in pre-amplifier stage in the AVR 7000, yet volume control is retained to the receiver's main L/R amps through these jacks as well. All he would need to do is switch it to "external processor/decoder mode," or however Harman Kardon has named it. A tape monitor out from the tube amp would result in a fixed output to the HK, while pre-amp outs to the HK will result in variable volume adjustment from both the receiver and the tube pre-amp.
I don't understand why you can't run..... 2 channel DVD>preamp>amp>main speakers......and.....remaining channels DVD>AVR>rear and center speakers. Why run the AVR back to preamp when the it can power the rears and center just fine?