(1) Good equipment will sound good at any volume, and you don't need a big amplifier to power your bookshelf speakers, however I would still recommend going with the balanced (XLR)interconnect option. (2) Depending on which amplifier was compared and which combination of source and speakers were used, and what your particular preference was, the only way to tell would be for you to listen for yourself. All that aside I would expect better sonic qualities from higher-end amplifiers and source equipment - this can be bad though because very good equipemnt can also end up revealing weaknesses in the remainder of your system, and, as in my case, you start snowballing into the world of high fidelity equipment.
