As the purchase of XM Satellite Radio by larger rival Sirius Satellite Radio Inc. closed Tuesday, questions remained about whether the combined company can handle its $3.4 billion in debt —- including $1.1 billion due next year.

Also murky was how quickly the two companies can mesh their technologies without angering consumers.

Sirius said radios that can play programming from both companies will be on the market within nine months. But most are sold for cars, and automakers are notoriously slow to integrate audio technology.

The nation's only two satellite radio companies have combined as Sirius XM Radio Inc. and will trade under the ticker symbol SIRI. Mel Karmazin, chief executive of Sirius, will take the same position at the new company.

Investors sold off Sirius shares Tuesday to their lowest price in nearly five years.

"The new company is going to face a lot of hurdles, operating as well as financing," said Tuna Amobi, a Standard & Poor's analyst.

He was disappointed by Sirius' accumulation of 280,000 net new subscribers for the second quarter, not as robust a figure as he had hoped for. Amobi is also concerned about higher interest payments.