AV Pre/Processor vs 2 Channel Pre-Amp - Sound Quality

A comment on your desired configuration.  If you are intending to run RCA/XLR to the subwoofer first, then take the high-pass output and connect it to your amazing 2-channel amp for bookshelves, you will probably not get any benefit from a dedicated preamp.  The analog stages in the subwoofer that crossover and output the high frequencies are not going to be as good as those found in 2-channel preamp, and even some high end HT Processors (such as the Classe SSP or Sigma).  You're pretty much degrading the sound quality by using the sub as a crossover/preamp for the amplifier.

If you really want a subwoofer and a dedicated 2-channel preamp, I would suggest using XLR output to go directly to your amp/bookshelves, then use the RCA output to go to the subwoofer to "support the low octave that bookshelves cannot reproduce".  It's not a perfect solution, but much better than your original thoughts.  The small bookshelves are going to roll off the bass frequencies anyways.

Oh, for integrated amp that has HT bypass.  The idea of an "HT bypass" is to completely bypass anything in the preamp, including any tone management or crossover.  The unit will typically connect the input wiring directly to the output wiring and not even go through the preamp stage, therefore letting the source AVR or HT Processor do the bass management on its own.

However, there is an existing solution that might help you.  The Parasound units, both the integrated and the P5 / P6 / P7 preamps, have a bass management crossover as well as full HT Bypass for left/right and subwoofer channels.  This allows you to still use a AVR or HT Processor and connect the 3 left/right/sub outputs directly to the Parasound unit for straight passthrough.

The Parasound integrated is a combination of the P5/P6 preamp and a version of the A23 amp with a larger transformer.  The Parasound amps have a warm sounding sonic signature (definitely on the warm side of neutral).  For the preamps, the P7 is the best unit due to better analog circuits and better power supply.

When you use the Parasound units for normal 2-channel listening (such as from a DAC or turntable), the Parasound unit will do the bass crossover management and send separate signals on the left/right and subwoofer outputs.  This gives you the best resolution possible.

I think both the Parasound Integrated and the Classe 2200i could be potential solutions. 

The Classe is going to have a superior DAC/preamp stage.  Much more resolution / attack / detail.  However, the amp part is Class D, which does has it's own unique sound.  And, like caphill stated, it does not have a phono preamp input -- and it's not a true analog preamp because it will convert all analog inputs to digital before processing.  All bass management is done in DSP and then sent to the units internal DAC.  Cost is higher, like caphill stated.  It's not a true "HT Bypass" preamp.

The Parasound is a true analog preamp.  Has a true analog crossover.  With phono preamp input.  Pretty much a "jack of all trades" integrated.  However, it is warmer sounding than the Classe with softer high frequency response.  But it's a true Class AB amp instead of Class D.  I suppose it's possible that the Parasound will sound more "analog" than the Classe, but it will be a "softer" analog.  The DAC that is built into the Parasound integrated/preamps is very low quality.  So it's best to use an external DAC for 2-channel audio.

Parasound integrated is much cheaper.  The previous version can be had used for $2k or under.  There's actually one on usaudiomart for $1700 right now.  The new HINT6 has some minor improvements (resistor ladder volume, increase phono gain), but not hugely significant.  HINT6 retail price is at $3k, so I suppose it's all about budget.

Not to get into an argument, but I have heard Classe's Class D solutions.  It is very clean/clear.  However, it is so clean that it's too clean.  There is no "life" to the music and it actually leaves me wanting more.

I suppose it's true that the Sigma can replace his receiver, but he needs to go into this with full knowledge.

Your statement that the Sigma does not have a "DAC" may be true in the conventional DAC chip sense, but there is always going to be a circuit that produces pulses based on digital data.  This has to go through some sort of pre-driver circuit for the amplifier.

I try to be very open minded when answering questions and not push one option over the other.  I have read many of your posts here and it seems that you push Classe solutions over every other solution out there, stating that Classe is the absolute best regardless.   I would ask that you try to post based on your direct experience with specific devices instead of "selling" the Classe marketing.  It really sounds like that's what your trying to do.