A sandwich adapter is effectively a wall or partition. It routes the oil out a port to whatever you attach to it ..and returns it on the other side of the wall via another port. It then goes into a full flow. The "wall" has a relief port in it (in the case of the Permacool) to limit the resistance/restriction of what you've attached to the ports. In the case of the Permacool, it limits this (typically) to 2PSID.
In the case of some higher volume oil flows, the poppet valve cannot bypass enough oil and it results in a lowering of post sandwich pressure. This is rare ..but if one needs to drill a hole to augment the capacity of the standard poppet port, it needs to be very small. Otherwise, you'll just bypass your installation after the oil warms enough.
Not all sandwich adapters work this way. Some, the Hayden for example, uses a bi-metal flat spring to close off a bypass port as the oil heats. I'm pretty sure that the oil flow would over come the spring tension in the event where there was a mismatch between visc and temperature of some inordinate amount at higher flow rates. I have not confirmed this, however.
If I interpret your second question correctly ..those are effectively spacers with ports. You can certainly use them if you're returning a bypass filter to a zero pressure point ..as in an access tap ..but they have no routing capability since they're not a "wall/partition" ..they're just a spacer and totally open on the interior.
To further anticipate where you're going, there's pretty much certain commerce blockades to doing stuff any cheaper. The most affordable sandwich is a Permacool ..as is the Permacool dual remote. The most reasonable sources for these items are jeg's and summit ..who both somewhat construct price fixing between them. You're looking at about $80 minimum to get both with the way they configure their flat shipping and handling fees.
If you're considering attempting to trump Amsoil with putting EaBp filters on a Permacool, you'll find a complete absence of remote mounts with the 1-16 thread ..unless they cost more than Amsoil's due to distribution. You can buy threaded adapters from a guy on Ebay, but he soaks you in S&H so that the final cost is about $20/each ..which turns your $3X.00 dual mount into a $7x.00 dual mount ..which is so close to a Dual Guard under the PC program it isn't even funny.
been there ...tried that. You may, with much work and time in research ..end up with a cheap Permacool for about $10 less than the high quality Amsoil mount.
