First off, there would be no issue using the Primaluna with the Song3's. My guess is that EL34 tubes would provide the highest sound quality, while KT-88's would likely deliver a bit more power (don't know this for certain but that is the case with many of this type of tube amplifier). In either case, I don't see any issues.
The allure of tube amplification is liquid smooth midrange. But as with all things audio, there is a trade-off. Tubes generally do not control woofers as tightly as solid state. So it comes down to whether you prefer smooth-as-silk midrange or tight, articulate bass. Neither is wrong. One is not necessarily better than the other. It all comes down to personal preference.
We've powered the Song3's with both and both sounded great in their own way.
I hope this helps.