Hmm. I'm confused now. The copy of the 4806CI manual I've downloaded from http://usa.denon.com/AVR-4806CI-OM.pdf
shows the same settings as the 3806 manual I downloaded. It says on page 55 that the LFE
setting in Surround Parameters affects DD, DTS, DVDA and SACD, and it's shown as available for MULTI CH IN in the table on page 157. And on page 100, SW Level
is said to only affect the EXT IN subwoofer terminal. I don't see any text about "you should not need this setting if using a Denon universal player".
I note there's also another setting shown "SW ATT", just for EXT IN, but it's not clear what that does exactly.
The way the manual describes it makes more logical sense than what you're seeing, as the terminology is correct - what you get over a digital link is plain LFE, not SW (LFE+redirected bass). So it should be an LFE control that affects it. But maybe they've implemented it so that the SW Level setting controls both the SW analogue input and the digital LFE input, leaving the LFE Level to only control the DD and DTS encoders. Hmmm. It would work, but it's not what that manual says.
I agree with your last assessment. The most sensible thing for a universal player to do is to align its SW/LFE outputs for all formats, by attenuating by 10dB where appropriate.
So, for DD/DTS/DD+/any other format that needs a 10dB LFE boost:
- Digital LFE out = raw LFE data off disc
- Analogue SW out = Lower5dB(LFE off disc + Lower10dB(redirected bass))
(The extra 5dB drop is needed to make room for the redirected bass)
For SACD/DVD-Audio PCM/any format that doesn't need a 10dB LFE boost:
- Digital LFE out = Lower10dB(LFE data off disc)
- Analogue SW out = Lower5dB(Lower10dB(LFE off disc) + Lower10dB(redirected bass))
So in the receiver LFE always needs a 10dB boost through digital and 15dB through analogue, regardless of format.
The only catch is that digitally lowering by 10dB will cost some quality, particularly for DSD (each re-encode of DSD introduces more noise). But I doubt you'd ever notice for the LFE channel.