Ok, let's see ..
My listening room is 12 x 8 x 3 = near 300m3. Yours (Han) is 400m3. That's 30% more.
My amps are 27 Watts. But, 27 for mid-high and 27 for the bass (the mid-high acts as a pre-amp for the bass).
With my DAC -which outputs 1.5VRMS- I play at -15dB for the softests albums (normal would be -27dB). Btw, of course I use the digital volume from XX - which I thought was an obvious solution, or I don't understand the question about that).
My speakers are 115dB.
The above really puts the room under pressure, and listening level is easily 90dB everywhere in the room.
While my problem is that I don't know the relation between needed dB and the volume of the room (hopely others or you can take the time to google it out), it would theoretically come to this when we only use distance :
Your room is 6M long, mine is 12. That needs 36dB (6dB per meter) more.
Your speaker is 92dB, mine is 115. That needs 23dB more.
Your DAC will be 2VRMS, while mine is 15, that needs 6dB less (not 100% sure about this one).
I play at -15dB at the most, so that's 15dB less. But, a that soft album can be boosted by 3dB (XX will do that). So 18dB less.
So we have 36 + 23 - 6 - 18 = 35dB you need additionally to what you have now, but which will be at the low side, because of the higher ceiling. Maybe the 30% because we already took into account the sqm roughly.
Even if with pre-amp your windows go out, I don't think a preamp will have that gain. You'll need a bigger amp ...
Maybe it is not fair to use all that volume, because at a normal listening distance things change drastically. But it is my opinion that the room needs to be under pressure if you really want to do it well, so YMMV. And like Nick suggested, you won't be able to listen nicely back in the room (might be the kitchen) which in my case really doesn't matter. SPL doesn't drop much, but first you have to have it loud enough.
Maybe first look for an amp, and next for a DAC ... Or keep on using the preamp and see how far you come with it (
)
Peter