The AD9244 + AD6620 function are integrated together in some of our latest converter products, for example the AD9695. In general you do not see stand alone digital down converters and filters as stand alone products (like the AD6620), they are either integrated into the converter or are implemented in an FPGA or digital ASIC. If the AD8138 was simply a buffer, then again products like the AD9695 include an integrated buffer. If you were using it for gain, you would still need to pick an appropriate amplifier to replace that block.
ADI also offers very highly integrated transceivers, like the AD9361 that can provide a higher level system solution.
