Using Krell rca & bal outputs for the same channel

I doubt they're missing, aren't they coming through your main speakers? You would certainly notice that big a gap in frequencies in any musical content. Just because there is an upper cutoff for the LFE channel doesn't mean that the output to the main LR channels has a low cutoff at that frequency.

This, of course, should be taken with a grain of salt, as I have an HT system, but don't really know how it works as a technical matter. But I hear plenty of lower frequency info from my main speakers on movies.

Rcprince has it correct. Remember, a subwoofer is just that...a SUB woofer i.e..below normal bass frequencies.

In music this is not an issue. The lfe does not get information above the crossover. My system crossover is 60hz.
However, if my processor doesn't create the LFE output like in music and if the LFE comes from an independent source other then existing channels then all bets are off. No 2+ channel PrePro in existence applies crossovers to the dedicated LFE channel.

In other words: Crossovers do not apply to the .1 channel.

If that is the case, then my sub gets the entire LFE channel. But my sub nitpicks on LFE freqs. This issue applies to any source that has a dedicated LFE.

Anyway, I am researching if Dolby and DTS mirrors the LFE in other channels. Since other channels also go down to 3hz, it would make sense that they would use LFE just for effects even though it is the other channels.
But I will be limited if someone has info in the LFE and no where else.

In my system, which is two channel, I use the RCA outs from my preamp to the sub. The sub's low pass filter is set at 50Hz. I use the balanced outs for my main speakers and they run full range. This works very well and there is no crossover to muck up the sound of my mains.

I did the exact same thing as Rwwear but had no preamp. The XLR outputs of the cdp were sent directly to the power amp while the rca outputs went to the sub. Both cdp outputs are variable so no preamp is needed. It was not difficult to get the sub adjusted to mate with the monitors using this configuration. You should have no problem going this route from the Krell preamp. Both the sub and the speakers are fed the full frequency spectrum with the sub crossover and level controls adjusted for a satisfactory blend.