Best way to integrate a subwoofer into Luxman Preamp + L-509X Integrated system?

I have the Luxman L-509X and it is an incredible sounding integrated amp, particularly once you give it a little volume. And when you get to higher volumes, it really starts to sing. I’m currently running dual SVS subs out of the pre-out on the back of the L-509X and everything works great (setting crossovers at the subs). Main speakers are Klipsch La Scala IIs.

At lower volumes when I am listening at night, the L-509X loses a little bit of its sparkle and depth, and I’ve found I can replace this by using my vintage Luxman CL40 as a preamp, and using the L-509X’s "Separate" setting (basically HT Bypass).

This bypasses the preamp and volume control in the L-509X, and allows me to use the CL40 into the "Main In" input as a tube preamp. At lower levels on jazz and acoustic music particularly, this adds incredible dimension and sparkle to the music.

Really a "best of both worlds" solution here, because the CL40 adds a good bit of distortion and grain at higher levels, and the L-509X excels at clarity, power, and dynamics at higher levels.

But the problem I’m running into is that if I’m running the subs out of the pre-outs on the L-509X, they are volume-independent from the CL40 preamp volume. So I have to manually adjust the subwoofer volume on the integrated volumen knob to roughly match where the volume level is on the CL40.

Running the subs from the CL40 Output 2 is not an option as it removes the subs from the L-509X for daytime listening and movie content, etc.

Running an alternate out from my Hegel HD30 DAC to the subs could be an option, but I’ve run out of outputs since I’m using the balanced XLRs out to the L-509X and the unbalanced RCAs to the CL40.

Is there any solution outside of using some post-analog DSP such as a Mini-DSP on the outputs that can give me subwoofer control tied to the main volume control regardless of whether I’m using the CL40 preamp or the L-509X as a standalone integrated?

Worst case scenario is I’m turning two volume knobs for matching between mains and subs when I’m using the CL40, but that isn’t ideal.
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Of course one argument could be that listening to jazz and acoustic music at low levels (via the CL40 preamp) shouldn't really require subs anyway :)

I am sure u read the above link.

i am going to use Legacy Wavelet’s DAC + Preamp + Crossover . You can check with Legacy if the preamp section can be bypassed.
Have you tried turning up the bass-treble tone controls for low level listening that is one of the reasons they are there.  
Might I suggest using high level speaker outputs instead of low level pre amp outputs to your sub(s); if of course your sub(s) have speaker level inputs.

In my case, since I did not have pre amp outputs from my integrated, I was forced to use speaker level connectivity instead of trying to level match with a fixed preamp output - which I tried with limited success.

In any case, using speaker level & utilizing my subs internal crossover to meet my speakers lowest frequency yields surprisingly excellent bass integration.

My bass quality is very engaging; give it a try if your subs can accommodate speaker level inputs.
I suggest use a automatic a/b line level switcher from MCM Electronics, when the CL40 output a music signal, the switcher will automatically switch its input from CL40 Output 2 to the subwoofer.

Thanks for the tips...

After running a side-by-side comparison again for several hours last night I came to the conclusion that the L-509X just sounds better using its own preamp. The CL40 will go...

I think it may be a matter of the L-509X just breaking in a bit more.

The distortion and hazier sound of the CL40 is too much of a compromise for its excellent front-to-back soundstage at lower volumes. 

Using the Loudness button on the L-509X, it is getting very close to a tube-like dimensional soundstage at this point in the break-in process. In an A/B comparison with both preamps at the same volume, the L-509X just sounds superior in every way (and already has the subs integrated).

I had a similar issue. I had the 509x and upgraded to the C-900u m-900u combo. What I did was to use my "B" speakers on the 509x and ran it to the back of my left and right SVS SB-4000 subs. That way your speakers and subs will act as one unit. 

With the C-900u it luckily has a XLR out so only one wire to each sub instead of two.
@atownkeep, ha, that’s how I was told my 509X went on the market (upgrade to 900u). Maybe I have your old 509X.

I’m running the left out of the pre-out to an SB2000 and the right out to an SB16 Ultra. Neither sub takes speaker inputs... So my mains are running ”full range,” but they are La Scala IIs, not capable of much bass below 58hz. I have the subs crossed over at 90hz and the integration sounds seamless.