need help with subwoofer setup. crossover related

Hi all

I need some help with the crossover setup for my subwoofer. My neat mf5 speakers goes down to 29hz -3db while my subwoofer crossover is only to 40hz at the lowest. So i have a overlapping of frequency. 

My amp and preamp have no subwoofer management and my subwoofer do not have eq. My squbwoofer ia the genesis g928 with dual 12inch woofers.

My room is acoustically treated with bass traps and diffusers. I am very satisfied with my 2 channel and was trying to achieve to the low 20hz ffrequency for pipe organ music and to increase soundstage.

I know many will recommend getting a external dsp like mini dsp or velodyne sms1...but there will be an extra cable to connect these devices to my main system. And therefore will effect the performance of my main system indirectly. 
What i desire is just to crossover the subwoofer to 30hz lowpass to blend well with my speakers. Or to crossover my speakers high pass to 40hz to blend well with my subwoofwrs. 

So is there any way i can externally or internally crossover my sub to 30hz without affecting the main performance of my current speakers?

Or is there any way i can crossover my speakers to 40hz without an external device? (Without the involving another set orlf ultra expensive interconnects)
Thank you all for the help and sorry for the long post.
My solution to a similar problem (in my case, incorporating a passive 15" Tannoy sub, along with another 12" sub). I use wye, or siamese connectors, for tapping into the L/R low-level signals for the two subs, at the preamplifier.

One signal goes to the 12" sub, the other to the Tannoy. It is here where I input the signal to a DBX 223 xs equalizer, (which can be purchased very cheaply), and from there to the amplifier for the passive Tannoy sub.

This setup works well for me, I get plenty of good clean bass, without affecting the two stereo channels' frequency response.

XLR to RCA adapters are necessary for the DBX unit, but they can be had for $8-$10 at Parts Express these days.

Best of luck, regards,
I have found that if you don't cross over high enough beyond the posted range of your main speakers your bass will be thin and more towards the outsides of the soundstage. My main speakers go down to around 30hz and the Sub instructions were to cross over just above where my mains drop off. Well I did this and my bass was very nicely integrated. I thought all was well. Then I heard the same speakers with a sub turned up to 60hz! And things really got punchy and full in the middle of the soundstage and made the sound a lot more well rounded. So I believe you should cross over a lot higher than many sub manuals state. The main thing is there is no SET number really, play with it and dial it in to YOUR liking.
Depending on the slope of the crossover, 40 hz might be just about right.
Thanks for all the input. Ill try crossing over higher. I tried crossing at 60hz and the midrange ia definitely effected.

If your source material is digital files, you could make these corrections in a program like JRiver Media Center. Unless I am completely misunderstanding how these setting work, you can go into DSP Settings > Room Correction and there you will find settings that route frequencies in a number of different ways.
Overlap can be dealt with via the phase control on the subwoofer amp.

I recently set up a system where the mains had a muddy bottom end but we didn't have a suitably high-quality highpass filter to roll off their bottom end. So I overlapped with the subs and put the subs out-of-phase with the mains. This not only resulted in a good blend and pretty much eliminated the buddy bass of the mains, but subjectively it seemed to clean up the rest of the spectrum of the mains a bit as well. I can't explain why.

We did use measurements to get it dialed in; would have been difficult by ear.

The crossover is not a brick-wall filter. You might try setting it to an octave above the 3 dB rolloff of your speakers, or even to the oft recommended 80 Hz. You might find it cleans up the sound if your amps and speakers are relieved of extreme LF duty.