Subwoofer channel mix + crossover

[OllBoll]

Hello there

I'm planning to include a subwoofer in my current 2-channel system:

DAC --> Volume control (Right) -->  amp --> speaker
                        (Left) -->  amp --> speaker

I plan to cross at ~ 34 hz since the speakers are floorstanders and the subwoofer will go down to 19 hz at -3 db.

First is a question on high pass PLLXO, low passing the subwoofer channel is of course a given but how about high pass on the regular channels?

Do I want to cross them with a high pass PLLXO to cross on both sides or would it it be better to simply choose the subwoofer crossover to coincide with the natural dropping slope at 34 hz of the speakers and skip the high pass filter?

Now the other question is what would be the best solution to include subwoofer by doing say A, B, or something else ( me wants info! )

A: Dedicated DAC for subwoofer:

DAC --> Volume control (Right) -->  amp --> speaker
                        (Left) -->  amp --> speaker

DAC -->            (Subwoofer) --> low pass PLLXO --> subwoofer amp --> subwoofer

If i understand correctly here the problem will primarily be timing issues, since it requires two separate DACs.

B: Merge channels into a subwoofer channel:

DAC --> Volume control (Right) -->  amp --> speaker
                        (Left) -->  amp --> speaker

                       (Right) -->  Transformer isolation --> low pass PLLXO --> resistor merge --> subwoofer amp --> subwoofer
                        (Left) -->  Transformer isolation --> low pass PLLXO --> resistor merge /\

The question here is: would this piggybacking and combining of left and right interfere with the ordinary non-subwoofer channels and worsen sound quality or would it not be a problem at all?

Thanks in advance
A curious Olle