When he joined Wilco in 2004, guitarist Nels Cline was already a star out in the margins, leading a prolific, acclaimed life in free rock and avant jazz as a solo performer, sideman and leader of multiple bands, including the Nels Cline Singers (it's an instrumental group). But even in a discography of more than 130 albums (so far), Coward (Cryptogramophone) is a rare adventure: a series of dreams and sound portraits, played by Cline on an overdubbed ensemble's worth of guitars, etc. Nearly half of Coward is taken up with "Rod Poole's Gradual Ascent to Heaven" — Cline's memorial for a late friend, which sounds like a room of John Faheys coming out of grief — and the suite "Onan," a wild high of hectic breakbeats, chunky noise and ecstatic psychedelia. "Prayer Wheel" and "The Divine Homegirl" are quieter spins through British-folk motifs and ECM ambience; "Thurston County" is a vigorous tribute to Sonic Youth guitarist Thurston Moore in Balkan wedding-song time with freak-rock lightning. Cline does all of the above when he plays with Wilco. But this is a chance to hear Cline's tone-color inventions, slashing ways in a solo and the melodies lurking even in his most challenging improvisations in a dramatic, often beautiful isolation.