Yes it’s fine.  It will have to be assigned a unique Sonos ‘room’ name and will appear in the controller as such.  But in the settings for this room just set the Autoplay room to one of your other Sonos ‘rooms’ and it will play fine.

If you never get wired speakers this will be a very expensive line in.

(You could get a decent pair of speakers second hand now, and sell them for not much less than you paid in a year or two, and upgrade to your ultimate speakers then.)

Thanks John! All up & running now. Just got to let the dust settle before I broach the subject of speakers with the ‘finance department’! ;) 

It’s interesting that you asked this question. In the very early days of vacuum tube audio, up to the late 1950’s and early 1960’s, vacuum tube amplifiers would often self destruct if the speakers were disconnected. This is the origin of the folklore that continues -- don’t run an amplifier without speakers. This vacuum tube amplifier fault was caused by improper design. The math required to create an “unconditionally stable” amplifier was not being routinely taught to young engineers. In fact the math was not fully developed until the mid 1940’s and was only available to a few at the PhD level. Until this math was discovered an unconditionally stable design was an accident. As transistors entered the market this math had filtered down to the undergraduate level and taught to a new wave of engineers who were designing unconditionally stable transistor amplifiers. Since these new engineers were not interested in the old fashioned tube amplifiers, the tube amplifier designs (by older designers) continued to be unstable. Finally, in the mid to late 1960’s new tube amplifier designs started using this math. It’s interesting that the early transistor amplifiers did not sound so good because of another math issue that was not pointed out until 1980.  This is the origin of the folklore that a transistor amplifier sounds bad. Transistor amplifiers don’t need to sound bad -- just do the math. Anyway, these math issues are now behind us, but if you discover an ancient tube amplifier in an attic, don’t apply power unless speakers are connected.