Hedge funds are filing their second-quarter moves this week, and it seems as if George Soros has a thing for streaming music platforms. Spotify (NYSE:SPOT) and Pandora (NYSE:P) were among the largest new purchases for Soros Fund Management this past quarter, accounting for $122.6 million and $56.1 million of the widely watched hedge fund titan's assets.

Spotify is the leading provider of premium digital music subscriptions. Pandora is primarily a haven for ad-tolerating freeloaders, but it's also making some major headway in getting more of its users to pay up for tunes. Buying big blocks of both companies doesn't necessarily mean Soros is backing up the truck when it comes to stand-alone digital music services, but it obviously means he believes both stocks will be trading higher in the future.

Singing a new tune

Spotify and Pandora have momentum on their side. Spotify hasn't made a lot of waves since its direct public offering. The stock opened at $165.90 on its first day of trading more than four months ago, and it's trading just 17% higher now. However, the stock is moving higher for the third month in a row as it closes in on new highs.

Pandora's been an unexpected rock star. Shares of the music discovery pioneer have soared 66% this year, rising as revenue growth is finally starting to accelerate after years of deceleration. That last statement can probably use some more color, as Pandora's back-to-back quarters of accelerating top-line growth to kick off 2018 is basically revenue growth going from 0.7% in the fourth quarter of last year to 1% and then 2.1% in this year's first two quarters. However, if you back out the revenue generated a year earlier from the Ticketfly event ticketing business it has since unloaded and the operations in Australia and New Zealand that have been closed down, the adjusted revenue would've risen a hearty 12% in Pandora's latest report.

Spotify is growing faster, and it also has two variations of its top-line growth. Revenue rose 26% in the second quarter on a reported basis, but it would've been 34% if you back out foreign exchange moves.

The one thing driving both stocks higher is that more and more people are approaching streaming music services as something that's worth paying for. Spotify's monthly active users have risen 30% over the past year to hit 180 million, but premium subscribers have soared 40% to close out the second quarter at 83 million.

Pandora's premium subscriber base has risen 23% to 6 million over the past year, but subscription revenue itself surged 67% in the second quarter. Pandora still has a long way to go to approach Spotify's 46% penetration rate of paying users relative to its total audience. Just 8% of Pandora's 71.4 million active listeners are paying users. The trend is still improving quickly at both companies.

The risks are there for both companies. Profitability remains elusive for both players. Investors will always have to be looking out for disruptive upstarts and tech giants that can shake things up in this niche, because even disruptors get disrupted. Soros is following momentum and the unmistakable trend of premium streaming music platforms, but both companies still have a lot to prove in justifying their recent gains.