I don’t see a problem using different subwoofers as long as they have adequate output for the high sensitivity of the Tektons. For the best overall sound, all speakers for the 7 channels should be timbre matched. For the absolute best sound, all 7 speakers should be identical.
http://www.soundandvision.com/content/matching-front-and-surround-speakers
http://www.avtruths.com/speaker.html