Anyone here tweak any Legacy Focus speakers?

That will require a complete crossover redesign.... not to mention finding drivers that are exactly the same size as what Legacy used unless you also want to modify the cabinet. Perhaps you would be better off letting the Legacy's go and finding something that might better work for you? (Legacy or otherwise...)

Why not just add a nice Rel Sub...I added two to my Dynaudio's for that extra lower bass extension with great results.Much easier than swapping out drivers.

I join others in strongly advising you to forget modding those spkrs. Too complex. Either add a sub & cut off yr Legacies around 50-70 Hz, or get different spkrs.

I have previously owned a pair of the pre 20/20 Focus and had no trouble getting bass extension well into the low 20's in my room. I thought their spec extension of 16 hz was optimistic but never found the bass extension lacking below 30 hz. I have not heard of other owners experiencing this either. I am wondering if the lack of bass occurs throughout the room or is just at the listening position. It seems as if speaker/listener position is causing part of the problem due to room modes. Have you tried moving the speakers and or your listening position? Six inches of movement can make all the difference with room modes. Also, tell us more about your room, set up, and amplification being used with the Focus.

For over 16 years I own a pair of legacy focus speaker.
The internal speaker wires and its terminations are the weakest link in these beautiful sounding speakers.

If you like the main characteristics or the signature of the sound of these speakers, and if you are aware that no matter what you do you are not going to change that, then I have a great advice for you.

The best way to improve the sound of the drivers is by replacing all the internal wires. You also have to get rid off its chip, poor quality terminations in the crossover area.

For the ribbon tweeter use "Unicrystal occ airlock" 18 awg wire
For the dome tweeter double up the run of the "Unycrystal"
For the Kevlar drivers use "Oyaide across 2000" (This is a vibration treated wire)
Keep in mind that all this wires are single cystal copper.
I have not done anything to the woofers yet.

As much as I like these speakers I knew that the upper frequency wasn't to open. Also I din't like the boxy sound of the middle range (Place your hands around your mouth like forming a tube and start talking and what are you are going to hear is what I call "boxy sound")

Now the upper frequency is wide open.
The middle range has more body and flesh, gone is the boxy sound.
The harmonics and the presence of the upper bass is honey for the ears.
The background is dead quiet and the sound across the board is more musical.

If the equipment let you hear the subtle details on how the artists inflect their voices (or any other instruments)as a way of trying to convey their feelings, then you will experience the raw emotions of this very intimate comunication.