Addressing your questions here, lets start with balanced/XLR.
If a unit/system is fully balanced, XLRs are superior. If the whole unit is not balanced, then there is a transformer that converts a single ended signal to an XLR. The quality of sound will be heavily driven by that transformer. For instance, the Musical Fidelity M6 line is fully balanced. It is at its best when the entire system including DAC is balanced. Alternatively, look at the Marantz MM7025. This is not fully balanced and has XLR connections. It is potentially better with single ended interconnects.
If everything in your system is fully balanced, including DAC, go balanced. If not, single ended is probably the way to go.
Integrated vs. Separates - This to me is easy. Unless you are looking at higher end gear, integrated amps are almost always the way to go. To me, the first separates I can think of that are worth buying new Are the Rogue RP5 and the Rogue Hydra or Stereo 100. That is a $6500-$7000 spend. I don't feel the lower end Musical Fidelity (M6) or Parasound (P5 and A21) are better in any way than the integrated amps they offer. This is my opinion and worth what you paid for it.
The nice thing about an integrated amp is that it is going to have a properly matched preamp and amp stage in terms of gain. Connections are short and will be well insulated. They tend to be extremely quiet. Where the tend to fall down is the internal DACs and phono stages.
I say all of this with a heavy bias toward separates as I have had separates for the past 25 years starting from Carver, Ayre, Rogue, PS Audio, Chord, Marantz and Art Audio. I have also owned a few integrated amps and have always been shocked at how good they sound. Micromega, Musical Fidelity, Musical Fidelity & Rega are a few.
I am not sure I can think of a tube preamp in the sub $3K range that I would pick over a $5K to $6K integrated amp new. There are plenty of used units that are very good. If you can find a used Rogue RP7 in this range, that would be one of my first choices.
If a unit/system is fully balanced, XLRs are superior. If the whole unit is not balanced, then there is a transformer that converts a single ended signal to an XLR. The quality of sound will be heavily driven by that transformer. For instance, the Musical Fidelity M6 line is fully balanced. It is at its best when the entire system including DAC is balanced. Alternatively, look at the Marantz MM7025. This is not fully balanced and has XLR connections. It is potentially better with single ended interconnects.
If everything in your system is fully balanced, including DAC, go balanced. If not, single ended is probably the way to go.
Integrated vs. Separates - This to me is easy. Unless you are looking at higher end gear, integrated amps are almost always the way to go. To me, the first separates I can think of that are worth buying new Are the Rogue RP5 and the Rogue Hydra or Stereo 100. That is a $6500-$7000 spend. I don't feel the lower end Musical Fidelity (M6) or Parasound (P5 and A21) are better in any way than the integrated amps they offer. This is my opinion and worth what you paid for it.
The nice thing about an integrated amp is that it is going to have a properly matched preamp and amp stage in terms of gain. Connections are short and will be well insulated. They tend to be extremely quiet. Where the tend to fall down is the internal DACs and phono stages.
I say all of this with a heavy bias toward separates as I have had separates for the past 25 years starting from Carver, Ayre, Rogue, PS Audio, Chord, Marantz and Art Audio. I have also owned a few integrated amps and have always been shocked at how good they sound. Micromega, Musical Fidelity, Musical Fidelity & Rega are a few.
I am not sure I can think of a tube preamp in the sub $3K range that I would pick over a $5K to $6K integrated amp new. There are plenty of used units that are very good. If you can find a used Rogue RP7 in this range, that would be one of my first choices.