Transformer coupling was a standard practice on the early units. It is still done by some, but be careful not to push the voltage increase too far. High turns ratios - above about 6dB gain - will increase distortion.I use piezo tweeters on the smaller entry level speakers that are only about 96dB/M/W. So I don't need to increase their sensitivity. But if I were to consider the use of transformers, I would not go much past about 100dB/W/M. If higher output is needed, I'd go with a different tweeter than the KSN1038 or similar units.