Well, found an interesting thread on the Hi-Rez Highway discussion board:

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Posted by Martin , on January 12, 2004 at 07:44:04
In Reply to: Re: Denon 5900 - Source Direct or Bass Mgt posted by timm on January 12, 2004 at 06:09:58:


But, with SACD playback specifically, the LFE is suppressed by 15dB when you have source-direct set to "off". So even you have engaged the 10dB LFE boost setting, you’re still 5dBs short, compared with the "Source Direct" mode. That could account for differences you hear.
In addition, I would expect that source-direct will involve a shorter signal path (by avoiding certain processing steps) and this could (perhaps) improve the sound.

N.B. as you may know, one-bit DSD data does not take kindly to any form a post-processing — even if that is performed in the "pure DSD" domain, as is reported for the -5900’s bass management. So maybe even DSD-bass management is audibly degrading the signal slightly?

On the other hand, DVD-A’s PCM signals tend to have a much easier time with operations such as bass management when performed by a hi-bit integer DSP (two 32-bit Sharcs in the -5900).

N.B. The other thing to note about "source-direct" is that one would use it for full-range six-channel music, where you have six identical large speakers encircling you (and no sub, of course). For example, the DVD-Audio label "MDG" does precisely this with its 2+2+2 concept. e.g. center & sub channels as used for "height" information.. I would imagine there are SACDs also which have a similar configuration. I think Telarc’s 1812 is one.

>> since I definitely need the sub - source-direct kills that for two channel listening - any way around this - other than going into the menu and flipping source direct off? thanks tim. <<

I'm not sure, but I don't think so.

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It seems like I stumbled on to the correct solution to my subwoofer problem with 6 channel analog DVD-A and SACD listening. I did listen to a DVD movie last night (i.e., digital input on the 950) and all sounded superb.

Thanks again!

Mike