In the 990 setup screen, I kept the speaker xover settings as they were -- these settings have worked fine for some time for both stereo listening and home theater listening:
Front L/R: 40 hz
Center: 40 hz
Rear: 40 hz
I didn't change speaker size either:
Front L/R: Large
Center: Small
Surr L/R: Small
The 220's are pretty hefty speakers. Their -3dB point is a good 5Hz lower (or more) than my old Paradigm towers. That being said, now that you have a sub, you might want to experiment with running the fronts as "small" and using either the 40Hz or the 60Hz crossover point. The center and surrounds both deserve to use the 60Hz crossover point, as the 40Hz crossover is almost directly at the center's -3dB point and actually about 5Hz below the surround's -3dB point. You could even experiment with the 80Hz crossover point for those.
For my first attempt to configure the sub, I set Subwoofer to "LFE Only", which the instruction manual says "If you have very large front speakers, you will probably get the best results with the 'LFE Only' setting." It doesn't say anything else about this setting, nor does it define "LFE" though I can assume from context it's low frequency something or other. My front speakers aren't really HUGE but I wanted to see what happened. Result: No signal whatsoever being sent to the sub. None. Zip. Zero. Not my 20hz test tone, nothing.
The LFE signal is the ".1" channel of 5.1 sources - it stands for "low frequency effects." When set to "LFE Only" the sub only gets that channel. Any test tone played to the fronts will go solely to the fronts when they are set to large and the sub is set to LFE only.
So then I switched Subwoofer to "L/R+sub", which the manual states "blends some of the bass from the left and right speakers to the subwoofer." When I did this, the sub kicked on and performs like a champ with 20hz, 60hz, normal music, etc.
Just curious why "LFE Only" doesn't allow any signal to go to the sub -- what is the point of this? And does it seem like "L/R+Sub" is the correct option for me?
The "LFE Only" option only exists when using fronts that are set to "large". It is actually the most pure option for this scenario, as none of the low frequency audio being sent to the front speakers is duplicated in the sub and no speaker is asked to play frequencies lower than it can reproduce comfortably. You've told the 990 that your fronts can handle everything when you set them to "large", so it does exactly that. Only the dedicated subwoofer signal - the LFE channel - goes to the sub. The "L/R+Sub" option is there as a way to produce what's sometimes called "double bass" - the low frequencies still go to the fronts, but they
also go to the sub, so two speakers are reproducing the same audio and "doubling up" on those frequencies. In reality, the fronts are rolling off. With a 40Hz crossover set for the "large" fronts, there's not a lot of overlap.
Which is right? Personally, I'd suggest spending some time running the system with the fronts set to "small" and the crossover points I mentioned earlier. This could be considered the most "proper" approach, since even those big Dynaudio towers aren't truly "full range" (which would mean flat down to 20Hz if taken literally). In this scenario, the sub will simply be on, with no option for "LFE Only" or "L/R+Sub". On the other hand, there is no one right answer. The goal is to produce sound that pleases you. If running large fronts and the sub set to "L/R+Sub" pleases your ear, do it.
SACD through the 7.1 analong inputs works with the sub too -- I dont' know that "LFE" and "L/R+Sub" apply when using 7.1 as the input mode; I assume the ".1" sub information in the 7.1 signal overrides both of these settings (?).
Haven't tried DVD/BluRay yet to see how 5.1 surround works. Again, not sure that "LFE" and "L/R+Sub" apply for this. I assume the ".1" information in the 5.1 signal overrides both of these settings. (?)
If it's a multichannel SACD, there's probably an LFE channel. Same for DVD's and Blu-ray Discs. That LFE channel will go to the sub no matter what else you do. Redirected bass from the fronts may or may not, depending on your settings (large fronts and "L/R+Sub" and small fronts will both send bass from other channels to the sub). The bass management settings still apply for the 7.1 analog input as long as you don't set all speakers to "large". They also apply to any digital audio input.