You were right about adding a sub.

it's been my experience that high passing the mains has a tremendous effect on the entire frequency range and is absolutely my preferred method of integrating a sub (rather than playing the mains full range and bringing the sub in at the roll off point of the mains).  getting the timing / phase relationship right via careful placement of the sub or time delaying the mains will make the integration absolutely seamless.  when it's right, everything just snaps into focus and the sub completely disappears.

If you want to play with delay/timing between your mains and a sub, I'd suggest a digital crossover.  I mess about with a Behringer DCX2496...variable timing, slopes, types, points, whatever boats your floats....
Inexpensive, too.  Yes, I know...it may not have any 'pedigree' by the cognoscenti, but It Works.  "OMG, it's 'digital'!  It Must screw up analogue!"

Oh, get real, y'all....unless you've been living under a rock and Everything you listen to is ancient vinyl, digital is pretty much the gorilla in the room.  But, I'm not addicted to dead white Euro composers, either.  Nor do I believe that my 'system' needs to rival the price of the average condo to please me....

MHO...and everything I know is 'wrong'.  Doomed to 'audio hell'.  Oh, well...I know the bouncer, he lets everyone in anyway....*L*

I could not be more thrilled with my pair of Vandersteen 2Wq subs with battery-biased crossovers.  They have the same effects listed by the o.p., and are totally transparent and they blend seemlessly with my mains.  When you get that ---- eating grin on your face while listening, you tend not to want to change a thing!

I appreciate everyone's comments. The Sound Cylinder sounds pretty good in the blend- but I'm still dialing it in.

My aging Mirage dual 8" sub sounds great in my bedroom system. I've been reading up on subs designed primarily for music and I'm likely to go for something to replace the Svs, and return it to my home theater setup.

Vandersteen and Rythmik are interesting to me. Of course Rel and Jl Audio are popular.

I like the option to cut the low end frequencies to my mains. I think I may be limited to speaker level connections to accomplish this, since my Integrated does not have an amp in option- but it does have pre-out jacks. 

Avsjerry- I like the opportunity of the Behringer - but it is way beyond my level of expertise.

There is probably a way to cut frequencies to my mains without using speaker level inputs. Once I get close to deciding on a model, I'll call and try to educate myself.

Such a great hobby! My girlfriend is getting more and more interested in audio and seems to increasingly enjoy music. 

Thanks again!

A great way to high-pass filter your mains is to install a single capacitor at the input of the power amp (or power amp section of an integrated). The value of the capacitor determines the corner frequency of the filter (3dB down point), and the roll-off rate will be 6dB/octave (1st order). The formula for frequency versus capacitor value can be found on the net, and includes the power amp's input impedance.