Question about making 2.1 home theatre work

I've been using a Panasonic XR45 receiver for 2-channel HT for a few years. I tell it "no center, no surrounds, no sub" and it mixes down to 2 channels and sounds very good taking digital coax from DVD and toslink from TiVo.

Now...I want to put a REL sub into the system. The great thing about REL subs is that you can use them simultaneously for .1/LFE and to augment bass from your other speakers. But it appears that once I tell the XR45 that I have a sub, it insists on sending everything from 100 Hz down to the REL, whether it is LFE or not, and probably filtering the signal to the front speakers. That's not what I want to do. I want to continue to run the front speakers full range (I may eventually augment them off the speaker taps using the REL Speakon connection) and just use the sub for the .1 channel only. Is this possible to do with AV receivers -- to distinguish the .1 channel from the low frequency content in the rest of the mix? Am I missing something, or am I up against a limitation of the Panasonic?
Might be the Panasonic's limitations, with Rotel you can configure the sub at many cross-over points, full range fronts PLUS sub if you wish and even define music and game modes for sub or no sub use, many new recieveres can do more than your Panasonic can, sorry to say but Panasonic isnt exactly a big player in the reciever market.
Just use the speaker level connections to your front speakers, what it duzzent know won't hurt it, mums the word, matey....aaarrrrrr!
I thought that you told the AV receiver that your left & right speakers are LARGE and they will be run full range. Though I have no idea why anyone would want to do this. Bass management in AV receivers is such an advantage in 2.1 music systems.
Bob, I did tell it they are large, but I think that when I also said I have a subwoofer, it automatically starts using it. A good question would be, how can I test for bass content that is LFE only?

Jalanc42069 -- I don't get your meaning. If I use the speaker level connections, then I get the augmentation I don't want and I don't get the LFE I do want.

Perhaps I misunderstand the .1 concept. Better pull out Harley's book and read up.

Chadnliz, I know Panasonic is lightweight in this space. But since I don't use the receiver for video switching and I don't use surround channels, it suits me fine. This model was quite an item on the forums a few years back and, I think, deservedly so. For $249, it sounds very nice with digital signals.

Thanks guys.
Drubin, I think you can get the proper test signals from any certified THX DVD -- THX Optimizer. Check the Subwoofer Crossover test.

My copy of Terminator 2: Judgement Day has the test signals.
Try what Jalanc42069 suggested. Tell the Panasonic, "no sub". Use the the high level connections that connect directly to the binding posts and set the cross over on the REL. Run your front speakers as large and set the x-over on the REL to around where your speakers naturally roll off.
As I said before, that doesn't get me the 2.1 I'm after. It may be the only solution, but it's not ideal.
My Marantz also seems to reduce the bass to the front pair of speakers when I tell it there is a subwoofer, even though I also tell it the front speakers are "large". I don't have any way to tell what the cutoff is though.