Good Morning Andrei,
I imagine by now you've already moved on in one direction or the other on a pair of speakers, but in the event you are still pondering....
I do own a pair of Paradigm Tributes which I purchased from a dealer out of France in 2014. They are truly amazing, and the very few professional reviews which do exist are not exagerations. To specifically address your questions though:
I find them to be very flexible with regard to rear wall placement. While I am surprised that with such a huge room, you can't pull them 20" out, you should be fine at 12", so long as the left/right flanks of the speaker is not confined by furnishings. They will need to breathe, especially if placed closer to the back wall. Mine are currently at 16" from the rear wall, and I found that their toe in angles are far more critical to their performance than anything else, with regard to placement. Most professional reviews of Studio series and Signature Series make detailed mention of how Paradigms toe-in greatly impacts their performance, and I've found that to hold true of the Tributes.
With regard to your tube amp, I would caution you there. Yes, Tributes are highly efficient, and yes, I have been pondering going with a tube (Carver Cherry or Pass Labs are my primary considerations at this point), as I have come to believe they would perform beautifully with the right tube. However, you may find 65W too light from a tube for this speaker, given your room size (especially if it is carpeted!). I have not done any reading on your amp, other than coming across mentions of it in the chat rooms, so I am not very familiar with its strengths/weaknesses/etc ... but given a tubes propensity to be light, or not tight, in the bass arena, a higher power tube, or a tube known for unusually high quality bass, would be my recommendation. Or, a set of used, hi quality, inexpensive solid state amps to bi-amp would be another solution,,,using the solid state for the bass only... used rotel or monoprice monolith comes to mind that would fit the bill very nicely and affordably.
Either way, I can tell you, if you did, or you will, pull the trigger on the tributes, I don't believe there would be any way you could be happier without jumping to a $16,000 pair of Revel Salon Studios, or maybe...maybe ... a pair of $9000 Paradigm Sig S8. The tributes are better than the Sig S8 in many regards, though the Sigs will give slightly greater depth to music, and more bass punch (though tributes bass is more refined and tonal in nature). Honestly the Revels would be the very first speaker in the price band that one could honestly say does everything as well as the Tributes, and does 1 or 2 things better. Plus up of 10 grand (166%) to do 1 or 2 things better, while towing the line on all other areas, is one hell of a compliment to the Tributes. Throw in that you could not drive Revels with a tube amp unless it was one of the elite massively powered tubes with serious bass drive, and I really don't thing one can go wrong with the Tribute, unless you prefer your music to sound completely laid back. These are musical speakers which breathe life into a room.
One final note...I've found that given the revealing nature, and 3 dimensional staging ability of the Tributes, they are highly reactive to Speaker Cables...in that they truly bring out whatever the cable is doing, or capable of. For example...I started with Kimbers, and found them very dry sounding through the Tributes. I moved to lower priced Blue Jeans my brother lent me, and enjoyed their balance and musicality, though my gut told me there was much more to be heard. I moved to MIT3....these were beautifully warm while still accurate and detailed, though not as detailed as the Kimbers. While I was very pleased with the sound of the MITs, I knew there had to be a way to get the warmth and the detail, and was realizing the Tributes would show me every nuance of the equipment and cables. To experiment further, I then went to Silnote Morpheus II Ser II and found them amazing, neutral, spacious, with the only very very slight downside of being almost too detailed....every so slightly too crisp, because of how revealing the Tributes are.... I called back to Silnote 2 months after purchase, and they let me trade-up with a 100% return credit to the Poseidon II....NOW I am in complete heaven. All the detail of the Morpheus without any tinned sounding edge, with the Warmth of the MITs, and a musicality and soundstage I've never experienced before.
I imagine by now you've already moved on in one direction or the other on a pair of speakers, but in the event you are still pondering....
I do own a pair of Paradigm Tributes which I purchased from a dealer out of France in 2014. They are truly amazing, and the very few professional reviews which do exist are not exagerations. To specifically address your questions though:
I find them to be very flexible with regard to rear wall placement. While I am surprised that with such a huge room, you can't pull them 20" out, you should be fine at 12", so long as the left/right flanks of the speaker is not confined by furnishings. They will need to breathe, especially if placed closer to the back wall. Mine are currently at 16" from the rear wall, and I found that their toe in angles are far more critical to their performance than anything else, with regard to placement. Most professional reviews of Studio series and Signature Series make detailed mention of how Paradigms toe-in greatly impacts their performance, and I've found that to hold true of the Tributes.
With regard to your tube amp, I would caution you there. Yes, Tributes are highly efficient, and yes, I have been pondering going with a tube (Carver Cherry or Pass Labs are my primary considerations at this point), as I have come to believe they would perform beautifully with the right tube. However, you may find 65W too light from a tube for this speaker, given your room size (especially if it is carpeted!). I have not done any reading on your amp, other than coming across mentions of it in the chat rooms, so I am not very familiar with its strengths/weaknesses/etc ... but given a tubes propensity to be light, or not tight, in the bass arena, a higher power tube, or a tube known for unusually high quality bass, would be my recommendation. Or, a set of used, hi quality, inexpensive solid state amps to bi-amp would be another solution,,,using the solid state for the bass only... used rotel or monoprice monolith comes to mind that would fit the bill very nicely and affordably.
Either way, I can tell you, if you did, or you will, pull the trigger on the tributes, I don't believe there would be any way you could be happier without jumping to a $16,000 pair of Revel Salon Studios, or maybe...maybe ... a pair of $9000 Paradigm Sig S8. The tributes are better than the Sig S8 in many regards, though the Sigs will give slightly greater depth to music, and more bass punch (though tributes bass is more refined and tonal in nature). Honestly the Revels would be the very first speaker in the price band that one could honestly say does everything as well as the Tributes, and does 1 or 2 things better. Plus up of 10 grand (166%) to do 1 or 2 things better, while towing the line on all other areas, is one hell of a compliment to the Tributes. Throw in that you could not drive Revels with a tube amp unless it was one of the elite massively powered tubes with serious bass drive, and I really don't thing one can go wrong with the Tribute, unless you prefer your music to sound completely laid back. These are musical speakers which breathe life into a room.
One final note...I've found that given the revealing nature, and 3 dimensional staging ability of the Tributes, they are highly reactive to Speaker Cables...in that they truly bring out whatever the cable is doing, or capable of. For example...I started with Kimbers, and found them very dry sounding through the Tributes. I moved to lower priced Blue Jeans my brother lent me, and enjoyed their balance and musicality, though my gut told me there was much more to be heard. I moved to MIT3....these were beautifully warm while still accurate and detailed, though not as detailed as the Kimbers. While I was very pleased with the sound of the MITs, I knew there had to be a way to get the warmth and the detail, and was realizing the Tributes would show me every nuance of the equipment and cables. To experiment further, I then went to Silnote Morpheus II Ser II and found them amazing, neutral, spacious, with the only very very slight downside of being almost too detailed....every so slightly too crisp, because of how revealing the Tributes are.... I called back to Silnote 2 months after purchase, and they let me trade-up with a 100% return credit to the Poseidon II....NOW I am in complete heaven. All the detail of the Morpheus without any tinned sounding edge, with the Warmth of the MITs, and a musicality and soundstage I've never experienced before.