Possible sound deterioration adding subwoofer between amp and speakers

B&W CDM1 is a two way? It would benefit from higher crossover, 80hz, or even up to 120hz. Just put the sub between the two speakers. Also, make sure you have bass management to cut the low frequencies from the speakers + time align them.

Thanks, Eric. Because I anticipated that the best and most appropriate response to my post would be, as you said, to try it and see, I did just that. I was hoping that when the it was connected that the crossover only affected the frequency at which point the sub was activated and the main speakers would receive a signal as a simple pass through.  I still don't know whether that's the case but, even though my ability to discern subtle sonic variations , there was a reduction of sound quality that even I could tell. This was the case no matter if the crossover was in the circuit or bypassed, whether the sub's amp was on or off, its volume was set to zero, regardless of the crossover setting or if the sub is plugged in or not. 

So, I got my answer, the sound is better without it. Whether the culprit is nothing more than that caused by additional connection interfaces or something a little more involved, makes no difference; it just doesn't work for me. Thanks again for your response. 

Thanks, Coli. I got your post as I was responding to Eric. At this point I'm going back to what was working so well. 

I had read this info on their website before I started this experiment and chose option #2. What you're suggesting makes sense and I had even thought of trying that. After all, when I built my first amp in the late fifties I simply paralleled my bass driver with no crossover across the output posts of the amp. Back then, though, I hadn't even considered impedance as an issue. With this configuration, though, it is a concern. I'm sure the impedance would be lowered and this amp does have 4 ohm posts, but my experience with tube amps is limited and I don't know what the current draw increase would be or to what extent it might exceed the capabilities of the amplifier. 

broadstone, I have a Pinnacle Baby Boomer sub (acutally 2).  I run them with Newform Research monitors.  I tried the speaker level route and the sound degraded horribly.  The crossover and slope are It is much better to run at the rca line level interconnects in parallel with your speakers (use a y splitter if you don't have two outputs) and adjust crossover point and gain by trial and error. Depending on your components, try the 180 degree phase switch.  The Baby Boomer is nice little sub for its price point and its sealed design results in tight bass if not overly deep and loud.  I use two in my setup and it makes for a much smoother integration.

I think I have an idea that might work, at least it did when I was using a preamp in my main system. I'll use 2 RCA splitters from the Dragonfly sending duplicate pre amplified signals to both the amp and the sub. The amplifier is integrated and the sub is powered, even for non line signals, so I think this will work and impedance issues will no longer be a factor. I'll get the stuff I need and report back unless one of you sees othe issues that might be seen as a problem. 

It worked. The signal to the amp seems clean and the sub is working ok. The rest of the story is that I used a splitter combining R and L signals from the DAC to the mono line input of the sub. If the sub's power switch is on, regardless of the position of either the volume or crossover controls, the sub is audibly on and its volume control is fully functional.  Obviously,with the sub's switch off, the setup returns to the same uncluttered great sound that led me to buy this amp in the first place.  Anyway, I'm satisfied and thank Those who helped me with this question.