If your bass is passive, I would recommend putting the buffer at the beginning of the chain, and making sure that the particular buffer you choose has a high input impedance (at least 1 Meg). Like A8 said, shorten that first cable from the bass to the board if possible.
Remember that not only does every patch cord between pedals add to the capacitance dragging down your tone, but each one of the plug and jack connections adds capacitance, as does every mechanical bypass switch. You could have the capacitance equivalent of like 50 feet of cable just on the pedalboard. All of the cords, plugs, and switches also can get dirty or poorly-conductive, causing further problems.
Sometimes the problem is a "bad buffer" like people commonly blame on Boss or other mainstream inexpensive brands, but sometimes it's a cluster of a large number of small interferences that add up.