Occasionally I am contacted via the message system regarding someone wishing to try Schroeder Method, and they ask about a particular assemblage of gear, whether it will be safe to try. My answer continues to be review the original article (Audio Blast: Schroeder Method of Interconnect Placement at Dagogo.com), the threads here in regard to it, and contact your manufacturer to inquire about whether it is safe.
To date I have not heard of any incidents with incompatibility or damage to gear. My best information tells me that this is patently safe, as it would merely half the impedance and double capacitance. The admonition is that this should not be used with very long ICs as it could be a problem for some preamps to drive. I have been told my more than one manufacturer that an IC of about 1m would not present any problem. I typically double up 2m ICs and have used two instances in systems regularly (i.e. between source and integrated DAC, and between integrated DAC and amp(s). I have heard concern regarding use of the Schroeder Method when using an NOS DAC (output driven from a chip) or a Class D amplifier. However, I know that TEO Audio has used a Red Dragon class D amp successfully. I would like to try it with an inexpensive class D sometime.
The warnings have largely been theoretical, however, manufacturers have a right to state what would or would not void a warranty.
Most gear seems perfectly content with Schroeder Method. I have used Belles, Benchmark, Exogal, First Watt, COS, Redgum Audio, Eastern Electric components all successfully. They all have sounded far superior using Schroeder Method. I am also using another well known amplifier, and a different manufacturer’s preamplifier, currently with Schroeder Method successfully (but they are under review and I do not wish to disclose them at this time). I regularly use Schroeder Method for both RCA and XLR, and both work equally well with it.
The body of information seems to be growing that the doubling of ICs is benign to most gear. Every instance that is tried is helpful information to learn about it. I imagine there could be some bizarre combination of gear that might be incompatible, so the warning stands. However, so far, all systems I am aware of that it has been tried have been without harm.