Joint spectrum and signal coordination is a promising dynamic spectrum management (DSM) technique to significantly boost data rates in vectored DSL systems. This paper presents a novel low-complexity algorithm for joint spectrum and receiver signal coordination in upstream DSL transmission. The algorithm is referred to as MAC-DSB and can be used for both a MMSE-GDFE and a linear MMSE receiver. MAC-DSB consists of an improved dual decomposition based approach with an optimal gradient algorithm for updating the dual variables and a low-complexity iterative fixed point update approach for tackling the decoupled subproblems. Huge reductions in computational complexity and good performance are validated through practical simulation results.