The following descriptions are mostly gathered from product briefs of the different SoCs.
All SoCs have in common that they don't actually contain the DSP for the xDSL line, but are connected to a "line driver", a separate SoC providing the physical layer adaption. They contain an ADSL core and an ATM Core for offloading most DSL/ATM protocol overhead.
First generation SoCs
The BCM6335 is one of the first ADSL SoCs from Broadcom and supports ADSL1.
The BCM6345 supports ADSL2 and has a PCMCIA interface, to be integrated in ADSL routers.
Second generation SoCs
An upgraded version of the BCM6335 with ADSL2+ support, USB 1.1 support as host and device.
An upgraded version of the BCM6345 with ADSL2+ support, support for a separate VoIP DSP. It is mostly combined with the BCM6301 line driver, but can also be combined with a BCM6505 VDSL transceiver.
It supports ADSL2+ through a BCM6301 line driver connected to the ADSL core and VDSL2 through a BCM6514 transceiver connected to the ATM core with a "utopia" connection. It seems to integrate an VoIP DSP.
Third generation SoCs
Low cost ADSL2+ SoC with integrated Switch.
ADSL2+ SoC with integrated wireless and DECT.
The current generation of Broadcoms ADSL SoCs, using a new architecture through a "bonding transceiver", supporting VDSL2/ADSL2+ and a second ADSL2+ connection simultaneusly.
Not a DSL SoC, but GPON.