@flavo - Hey Mike. Since you already have an amp/pre-amp and the 2-channel rig's front speakers, you can try the combo system now, using what you have. The only difference between using what you have now, is that you will need to set the volume control on your pre-amp to a pre-defined position, such as "top dead center" or "7" or whatever. Just remember that every time you choose the HT source, you'll need to set the pre-amp volume control to that pre-defined position.
So, with what you have today, remove the front L&R speaker cables and speakers from your HT receiver. Run a pair of interconnects from the L&R front pre-outs of the HT receiver into an unused line-level input on your 2 channel pre-amp. Turn on your HT receiver. Set your pre-amp source selector to the new input you are using for the HT front speakers, turn the pre-amp volume control to the pre-designated position, run your HT receiver's setup routine.
That should have you set up to power your L&R front speakers via the amplifier and speakers from your 2-channel setup.
The only additional complication of this setup, vs having a pre-amp with an HT bypass, is you have to remember which line level input you used for HT front and you need to set the volume control to the correct pre-designated position when you play HT, or the front speaker volumes will be off relative to the surrounds/center speaker.
I hope that make sense to you. Anyway, it doesn't cost anything to experiment. If you don't like it, put it back the way it was before.
Good luck, and enjoy.