Updated from 12:21 p.m. EST

EchoStar ( SATS) has acquired a significant portion of Sirius XM's ( SIRI) maturing debt and could seize control of the company's attractive assets, according to reports.

EchoStar, which sells set-top boxes and was the former parent of Dish Network ( DISH), has acquired part of a $300 million tranche of Sirius XM debt set to mature on Feb. 17, according to The Wall Street Journal, which cited people with knowledge of the situation.

The Journal went on to say that Charles Ergen's EchoStar could also be buying Sirius XM's senior bank debt, which comes due in May.

Shares of Sirius XM added 2 cents to 16 cents a share. Before the start of trading, the stock had been up by more than 50%. EchoStar added 43 cents, or 2.8%, to $15.83.

For Sirius XM, which recently reduced its total debt due on Feb. 17 to about $175 million, the future is a bit unclear. The company still has approximately $3.4 billion in debt, with just under $1 billion due before the end of the year, and its stock has fallen sharply since the July merger between Sirius Satellite Radio and XM Satellite Radio.

Additionally, a sharp tail-off in U.S. automobile sales, which is the bread and butter of Sirius XM's business, has investors worrying about the company's viability. Sirius XM has still yet to post a quarterly profit, and during its third-quarter earnings report, several key metrics for the company weakened, including net subscriber additions, the conversion rate of auto installations, and monthly churn.

EchoStar's investment further complicates matters for the company. The Journal reported that EchoStar could acquire up to 51% or more of Sirius XM's bank debt, force it into bankruptcy, and then take control of the company in the bankruptcy process. That is potentially very bad news for Sirius XM shareholders who have already owned the stock through a roughly 90% decline since the July merger.

"There is a lot of value to the satellites that Sirius and XM have up in the sky," said David Joyce, analyst with Miller Tabak. "There's value in buying the company simply for some of those assets on the cheap. Each satellite is generally worth $200 million to $300 million. While the equity value of Sirius being $500 million, and even though they have over $3.5 billion in debt, it makes the enterprise value about $4 billion."

Craig Moffett, senior analyst with Sanford Bernstein, argues that the physical assets may not necessarily be what EchoStar is targeting, if it is indeed looking to acquire Sirius XM.

"The issue, I think, is that this is potentially a very valuable franchise with a unique quasi-monopoly position in the automobile," Moffett said. "The company is starved of capital but not starved of potential growth. An investor with sufficiently deep pockets can buy what is potentially a very attractive franchise on the cheap."

Moffett said that Sirius XM is a perfect candidate for a takeover by Ergen, who has targeted several high-growth businesses in the past. In 2007, EchoStar was rejected in its attempt to take over Ion Media before acquiring Sling Media. Additionally, EchoStar was very active in the Federal Communications Commission's auction of 700-megahertz spectrum, winning a large chunk with $711 million in bids.

"No one understands the microeconomics of the satellite business like Charlie Ergen," Moffett said. "He knows the economics of the business as well as anyone on earth. He actively looks for opportunities to reinvest the cash that his business generates for a new growth opportunity."