To balance or unbalance that is the question

If you use balanced where possible you might reduce the chance of picking up some unwanted grundge, at least there.

Some gear is built with considerable effort put into the design and execution of balanced circuit topologies. One example of this is Pass Labs equipment. Unless this is the case, the general rule of thumb is that balanced circuits make the most difference when interconnect must be long (e.g. a long run from pre to amps), otherwise, the advantages are questionable.

I see nothing at all wrong with using the balanced inputs to your preamp, and using the single-ended outputs to your amp.

As far as great sonic benefits to using balanced, it would surely relate to your individual pieces of equipment. I don't have any balanced lines anywhere in my system, and I certainly am not feeling deprived of any "sonic goodness" because of that.

If your DAC and preamp have balanced topologies, then use the balanced outputs from your DAC. Since your amp has a single-ended topology, then use that output from your preamp. If the preamp or DAC are not using internally balanced topologies, and just have a transformer shoved into the line to provide a balanced connection, that is of no use whatever, in my opinion, unless you have some unusually long interconnect runs.