In the early days of satellite radio, the concept of being able to listen to music without having to listen to commercials was new to listeners, and Sirius and XM each used it as a cornerstone of their marketing efforts. But that was also at a time when the competition was really only ad-laden FM and AM music programming.

That's changed considerably over the past decade. SiriusXM (NASDAQ:SIRI) now offers not just music, but also a wide array of sports, news, talk, comedy, and special events, as well as music. It competes with streaming services as well at terrestrial radio stations. And much of the non-music programming it beams out -- including sporting events and TV news broadcasts -- already includes commercial breaks.

Sirius had been treading carefully on the advertising front, perhaps because the absence of ads was a big selling point in its early years. But it is growing its advertising, and executives seem to believe that there may be an opportunity to ramp that up.

"Optimistic about it"
Since 2009, the company has grown its advertising revenue by more than 95%, or better than 14% per year, compounded. Over the same period, subscription revenue grew by 55%, a compound annual growth rate of about 9%.

Even better, advertising revenue for the first six months of 2015 was up 17% year over year, from $47.7 million to $55.7 million.

But that still made up just 2.5% of the company's revenue, which is dominated by subscriptions.

Can Sirius continue to tap advertisements and grow that revenue into a more substantial contributor to the top line?

"Generally, I think the platform's matured as a true alternative vehicle for advertisers," Chief Content Officer Scott Greenstein told analysts last month. "It wasn't always that way, and it now is. So, we're optimistic about it."

Outpacing the competition
Market research would seem to back up that optimism. Sirius has been able to grow advertising much faster than brother broadcast media.

Revenue from spot ads on U.S terrestrial radio -- a nearly $14 billion market -- fell by about 4% between 2009 and 2014, according to the Radio Advertising Bureau.

That's the same period during which Sirius was able to nearly double its advertising revenue.

It's also been outpacing overall media advertising spending, which was up 5.3% last year, and 3.7% in 2013, and owing many of its gains to social media, according to eMarketer.

Fantasy sports have been an important driver for Sirius, executives said. But Greenstein said ad growth has been happening pretty much across the board for the company, "from all over sports, our news products and comedy, and some other things."

Where the opportunity lies
Terrestrial radio's strongest area of advertising remains the "locally focused, Main Street businesses who can directly observe the impact of radio advertising on their bottom lines," Radio Advertising Bureau CEO Erica Farber noted earlier this year.

Without a way to effectively target ads to users the way social-media networks or some streaming providers can, Sirius won't be stealing away advertising dollars from small, Main Street businesses.

But there's certainly more share for Sirius to gain. The media advertising market is expected to grow from $180 billion last year to $220 billion by 2018, a CAGR of 5.2%. Radio, meanwhile, is expected to continue to lose share in that market. And talk and news radio stations generated $1.5 billion in revenue in 2013, according to the latest numbers from media research firm BIA/Kelsey.

At a projected $110 million this fiscal year, Sirius will generate only about one-12th of what talk and news radio does across the U.S. With a growing audience and an ever-expanding lineup of sports, talk, and news stations, Sirius is positioned to continue taking share from terrestrial stations.

46 and a six-figure salary
Satellite has an audience that many advertisers covet. In an interview with Bloomberg earlier this year, CEO Jim Meyer described subscribers as "a little older and a little more affluent. ... They look like people who buy new cars, who on average are 46 years old and make $100,000 a year."

"As the [subscriber] base is growing and more and more advertisers are trying the product, frankly...they're getting the results they want ... and they keep coming back," Greenstein said.

Statista last year projected advertising revenue for SiriusXM through 2021. Those projections showed ads continuing to climb, but at a slower pace than they have been over the past several years. It sees ad revenue coming in at $176 million six years from now, or roughly 8% annual growth over the next six years.

Just not around music
Long term, that slower growth rate in ads may be more realistic. It's very unlikely that Sirius will begin selling ads around its music offerings, since the ad-free format gives it an advantage over terrestrial radio and free streaming services. You won't find mention of music channels on the company's webpage devoted to courting advertisers.

But if Sirius executives are right in their assessment of the growing advertising interest in its sports, news, talk, and comedy channels, it could present the company with a growing opportunity moving forward.