My standard stage setup is based on the 4-cable method and using the stereo input of the HX Effects to connect my two instruments (bass left, e-cello right), the HX Effects is configured such that I can switch on the fly between the e-cello and the bass. I use a heavily customized pedalboard (Pedaltrain Classic 1) hosting:

• HX Effects (Line6) (back)
• MS-60B MultiStomp for Bass (Zoom)
• Relay G30 receiver for bass signal (Line6)
• Expression pedal FP02 (Zoom) connected to the HX Effects
• Footswitch controller BFC-6 for the bass amp (Trace Elliot)
• Dunlop DC-Brick multi power supply

Pedalboard from underneath, left side (power in, power supply wiring), the front front (extra power out), right side (e-cello in (top), amp footswitch control cable, audio out, USB dongles for HX Effects and MS-60B), and the audio wiring.
Full description of the extensively customized pedalboard: pdf

A carry-on minimal stage setup is based on the pedalboard Nano from Pedaltrain. It is so small, it can be carried easily attached to a gig bag (total weight including bag and everything: 2.4 kg). Yet, it offers full functionality including the switching between e-cello and bass. Here the wiring of the audio signals. The tonal and volume adjustment between the e-cello and the bass is done using a Source Audio Programmable EQ. The actual instrument switching is done by a Behringer A/B Switch, the weakest device on the board as it is not as noiseless as I would like to have it. It is of course run in the "In 1/In 2 -> Out A" mode, the bass signal coming from a Line6 Relay G30 receiver goes into "In 1" (green LED •), the e-cello into "In 2" (red LED •). Then the signal goes through a Zoom MS–60B, which offers also a tuner. Then I use a Radial Passive DI-Box (StageBug SB-2), which offers an unbalanced THRU or balanced XLR actual DI output (Wiring). All powered reliably with a 1SPOT. Here a full description of the pedalboard, its design and building: pdf

My alternative stage setup has similar functionality, but it's portable and assumes I have not my big Trace Elliot amp with me (no footswitch controller on the board). The effects board is a Rockbag RB 23110 (dimensions 40.5 x 30 x 10 cm) from Warwick. It consists of:

• The signal from the bass ( Transmitter Relay G30 or Transmitter TB516 for Relay G70 ) arrives either at the wireless Receiver Relay G30 or Receiver Relay G70 from Line 6.
• The signal from the e-cello is a cable connection coming from the e-cellos lower output jack and entering the effects board input port IN1 (red dot).
• From there the e-cello signal leaves the OUT1 port on the effects board and goes to the 6-Band Equalizer (M109 MXR) from Dunlop.
• Both instrument signals go to the switch (AB100 Behringer) for switching between bass and e-cello playing. I use the switch in mode 'IN 1', 'IN 2' -> OUT A, i.e. the bass signal goes to 'IN 1' (green LED •), the e-cello signal to 'IN 2' (red LED •). 'OUT A' is the main signal leaving the effects case via IN2 port on the effects board before leaving the case via OUT2 port to very top right.
  Alternatively when the Relay G70 receiver is in use, I can use that as an A/B switch by scene switching. The e-cello being connected via cable uses the Aux In input on the Relay G70. The bass connects wirelessly. Unfortunately this introduces a delay when switching from the e-cello back to the bass, since the wireless connection is not upheld when the scene is switched to the e-cello input.
• Depending whether I use as the effect unit the Zoom B3n, the Zoom B3, or the POD X3, the effects board varies:
  with Zoom B3n (light weight) (Wiring diagram)
  This configuration uses the B3n bass effects and amp simulator from Zoom and the Relay G70 receiver (Line6). Moreover, the Bluetooth iRig BlueBoard fits onto the pedalboard as well, albeit having no connection to the pedalboard at all. I use it only to control the iPad mounted on the e-cello stand for playback (e.g. when using Anytune Pro+) or during score reading (e.g. with forScore).
  with Zoom B3 (light weight) (Wiring diagram)
  This configuration is centered around the B3 bass effects and amp simulator from Zoom, a great device. But on stage I was not happy with the cumbersome patch select mode requring 3 stomps to change a patch. Therefore I modified the Zoom B3 similar to what was described by AshBass on his great site and encouraged by the help of sledgehamer73 @ TalkBASS. Here all details on my modification of the Zoom B3 for patch select, rhythm and tap tempo.
  with POD X3 (outside board on amp)
  The POD X3 (Line 6) I typically set on top of the amp. The effects board then contains the foot pedal FBV Express MkII also from Line 6 to control my POD X3. I use then the POD X3 within the amp's effects loop.
  To have minimum weight on tour, notably when I have to bring along the effects board with my check-in luggage, I leave the POD X3 at home and favor the Zoom B3 variant.

and then of course...