If the report, which comes from Swedish paper Dagens Industri (translation), is accurate, it means Spotify is shooting for a valuation 76% higher than the $3B valuation it reportedly received in a ~$100M funding round last November. It also means the music subscription/Web radio service would be worth considerably more than Pandora (P - $3.44B market cap).
Spotify posted revenue of $577M (up over 2x Y/Y) in 2012, but also a net loss of $77.9M (+29% Y/Y), as massive content licensing costs (~70% of revenue) pressure its margins (Pandora can definitely sympathize). Thus, Spotify is reportedly looking to be valued at 9.1x 2012 sales. Pandora, whose own valuation has shot higher since November, currently trades at 8.1x FY13 (ended Jan. '13) sales.
Though many other firms rolled out subscription music services before it to limited success, Spotify appears to have cracked the code with the help of an intuitive UI, good music discovery tools, P2P tech that improves performance, and a cheap ($5/month) PC-only subscription option (PC/mobile subscriptions go for $10/month).
Spotify has 6M paid subs to go with tens of millions of free (ad-supported) users. Pandora has 2.5M+ paid subs and 72M+ total active users.