First Rate, First Class, Top Notch, Top Grade
noun, の adjective
This is a weird one. You have one stream. This is first rate stream material we have here, though. If you think about it, if you only have one stream (instead of a ton of streams), you can put all your effort and energy into it. When you do that, you're making sure it is a first rate stream in terms of quality and anything else.
いちりゅう
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
さすが、一流のピアニストは違うね。
That's something only first-rate pianists can do.
父は一流のピアニストで、たくさんのファンがいます。
My father is a first-class pianist and has many fans.
一流だろうが二流だろうが関係ない。私はあなたの作品を愛しているんです。
It doesn't matter if it's first class or second class. I just love your work.